. I y t' . '/'■■'./ wiWM. . v.;4-duVII3l48slM£K2Ami>«3»jii')«ftu NOTICES OF THE PROCEEDINGS AT THE MEETINGS OF THE MEMBERS OF THE Eo^al institution oi #reat Britain, WITH ABSTRACTS OF THE DISCOURSES DELIVERED AT THE EVENING MEETINGS. VOLUME X. 1882—1884. LONDON: PRINTED BY WILLIAM CLOWES AND SONS, LIMITED, STAMFORD STREET AND CHARING CROSS. 1884. patron. HER MOST GRACIOUS MAJESTY QUEEN VIOTOKIA. Uice^^^atron anti Jgonorarg J^emter. HIS ROYAL HIGHNESS THE PKINCE OF WALES, E.G. F.K.S. President — The Duke of Northumberland, D.C.L. LL.D. Treasurer— GEORGE Busk, Esq. F.R.S. — V.P. Honorary Secretary — Sir William Bowman, Bart. LL.D. F.R.S.— F.P. Managers. 1884-85. George Berkley, Esq. M.I.C.E. SirFrederickJ.Bramwell,F.R.S.— F.P. Joseph Brown, Esq. Q.C. Warren De La Kue, Esq. M.A. D.C.L. F.K.S.— F.P. Captain Douglas Galton, C.B. D.C.L. F.K.S. Colonel James Augustus Grant, C.B. p a T ff f? Q The Hon. Sir Wm. Kobt. Grove, M.A. D.C.L. F.R.S.— F.P. Riglit Hon. The Lord Claud Hamilton, J. P. {deceased). Sir Jolm Hawkshaw, F.R.S. F.G.S. Sir John Lubbock, Bart. M.P. D.C.L. LL.D. F.R.S.— F.P. Hugo W. Muller, Esq. Ph.D. F.R.S. Sir Frederick Pollock, Bart. M.A. — V.P. John Rae, M.D. LL.D. F.R.S. The Earl of Rosse, D.C.L. LL.D. F.R.S. — V.P. The Hon. Rollo Russell, F.M.S. Visitors. 1884-85. John Birkett, Esq. F.L.S. F.R.C.S. Charles James Busk, Esq. Stephen Busk, Esq. George Frederick Chambers, Esq. F.R.A.S. William Crookes, Esq. F.R.S. Rear-Admiral Herbert P. De Kantzow, R.N. William Henry Domville, Esq. Alexander John Ellis, Esq. B.A. F.S.A. F.R.S. Rev. John Macnaught, M.A. Robert James Mann, M.D. F.R.C.S. Sir Thomas Pycroft, M.A. K.C.S.I. Lachlan Mackintosh Rate, Esq. M.A. John Bell Sedgwick, Esq. F.R.G.S. Basil Woodd Smith, Esq. F.R.A.S. Charles Meymott Tidy, Esq. M.B. F.C.S. Professor of Natural Philosophy — John Tyndall, Esq. D.C.L. LL.D. F.R.S. &c. Fidlerian Professor of Chemistry — James Dewar, Esq. M.A. F.R.S. Jacksonian Professor of Natural Experimental Philosophy, Univ. Cambridge. Fullerian Professor of Physiology — Vacant. Keeper of the Library and Assistant Secretary — Mr. Benjamin Vincent. Assistant in the Library — Mr. Henry Young. Clerk of Accounts and Collector — Mr. Henry C. Hughes. Assistant in the Physical Laboratory — Mr. John Cottrell. Assistant in the Chemical Laboratory — Mr. R. N. Lennox. CONTENTS. -*^*- 1881. Page April 8. — Peofessor Tyndall. — The Conversion of Kadiant Heat into Sound .. .. ., .. .. 175 1882. Jan. 20. — William Huggins, Esq. — Comets .. .. .. 1 „ 27. — Reginald Stuart Poole, Esq. — The Museum and Libraries of Alexandria .. .. .. .. 12 Feb. 3. — Professor Tyndall. — Action of Molecules, Free and Constrained, on Radiant Heat {Abstract deferred) .. ,. .. .. .. .. 13 „ 6. — General Monthly Meeting .. .. .. .. 14 „ 10. — Professor Frankland. — The Climate of Town and Country .. .. .. .. ,. ..17 „ 17. — Professor John G. McKendrick. — The Breathing oi Fishes [no Abstract) .. .. .. .. 27 „ 24. — Professor Odling. — Sir B. C. Brodie's Researches on Chemical AUotropy .. .. .. .. 28 March 3. — Alfred Tylor, Esq. — Roman Antiquities recently found in London .. .. .. .. .. 29 6. — General Monthly Meeting .. .. .. ... 30 >j iv CONTENTS. 1882. Page March 10. — Joseph W. Swan, Esq. — Electric Ligliting by Incandescence .. .. .. .. .. 33 „ 13. — Eadweaed Muybridge, Esq. — Attitudes of Animals in Motion .. .. .. .. .. .. 44 „ 17. — Captain Abney. — Spectrum Analysis in the infra red of the Spectrum ,. .. .. .. 57 „ 24. — Professor W. E. Atrton. — Electric Railways .. 66 „ 31. — William Spottiswoode, Esq. — Matter and Magneto- Electric Action .. ,. .. .. .. 75 April 3. — General Monthly Jlkleeting .. .. .. .. 86 „ 21. — Professor Dewar. — Experimental Researches of Henri Ste. Claire Deville, Hon. M.R.I. (Abstract deferred) .. .. .. .. .. .. 87 ,5 28. — Professor Abel. — Some Dangerous Properties of Dusts .. .. .. .. .. .. 88 May 1. — Annual Meeting ,. .. .. .. ..114 „ 5. — Professor R. Grant. — The Proper Motions of the otars ., ., .. .. .. ,, IJLo „ 8. — General Monthly Meeting .. .. .. ..119 „ 12. — A. G. Vernon Harcourt, Esq. — The Relative Value of Different Modes uf Lighting (no Abstract) .. 120 „ 19. — Sir Frederick Bramwell. — The Making and Working of a Channel Tunnel .. .. .. 121 „ 26. — Sir Henry S. Maine. — Sacred Laws of the Hindus 143 June 2— H. H. Statham, Esq. — The Intellectual Basis of Music (no Abstract) .. .. .. .. 144 „ 5. — General Monthly Meeting .. .. .. .. 144 „ 9. — Professor Burdon Sanderson. — The Excitability of Plants and Animals .. .. .. .. 146 July 3, — General Monthly Meeting .. .. .. ..167 Nov. 6.— General Monthly Meeting 169 Dec. 4. — General Monthly Meeting .. .. .. ..172 CONTENTS. 1883. Page Jan. 19.— E. Bosworth Smith, Esq.— The Early Life of Lord Lawrence in India .. .. •• •• 183 „ 26. — George J. Eomanes, Esq. — Eecent Work on Star- fishes {iio Abstract) .. .. .. .. 184 Feb. 2. — Sir William Thomson. — The Size of Atoms .. 185 „ 5. — General Monthly Meeting .. .. .. .. 214 „ 9. — Moncure D. Conway, Esq. — Emerson, and his Views of Nature .. ,. .. .. .. 217 „ 16. — Professor William C. Williamson. — On Some Anomalous Oolitic and Palaeozoic Forms of Vegetation .. .. .. .. .. 220 „ 23. — Walter H. Pollock, Esq. — Sir Francis Drake .. 233 March 2. — C, Vernon Boys, Esq. — Meters for Power and Electricity ., .. .. .. .. .. 235 „ 5. — General Monthly Meeting .. .. .. .. 243 „ 9. — Professor George D. Liveing. — The Ultra-violet Spectra of the Elements ,, .. .. .. 245 „ 16. — Professor Tyndall. — Thoughts on Eadiation, Theoretical and Practical .. ,. .. 253 April 2.— General Monthly Meeting ,. .. ,. .. 266 „ 6. — Archibald Geikie, Esq. — The Canons of the Far West .. .. 268 „ 13. — Dr. Waldstein. — The Influence of Athletic Games upon Greek Art .. .. .. .. .. 272 „ 20. — Professor Baylet Balfour. — The Island of Socotra and its Eecent Eevelations ., .. .. 206 „ 27. — Sir William Siemens. — Some of the Questions involved in Solar Physics ,. .. .. 315 May 1. — Annual Meeting .. .. .. .. ..322 vi CONTENTS. 1883. Page May 3, 10, 17. — Professor Tyndall. — Count Kumford, Origi- nator of tlie Eoyal Institution .. .. .. 407 „ 4. — KoBERT H. Scott, Esq. — Weather Knowledge in looo .. .. .. .• •• •• oZo „ 7. — General Monthly Meeting .. .. .. .. 334 „ 11. — Professor Huxley. — Oysters and the Oyster Ques- tion .. .. .. .. .. .. 336 „ 18. — Professor C. E. Turner. — Kustarnoe Proiezvodstro ; or, The Peculiar System of Domestic Industry in the Villages of Russia .. .. .. ..359 „ 25. — Professor Flower. — Whales, Past and Present, and their probable Origin .. .. .. .. 360 June 1. — Frederick Pollock, Esq. — The Forms and History of the Sword .. .. .. .. .. 377 „ 4.— General Monthly Meeting 397 „ 8. — Professor Dewar. — The Electric Arc and Chemical Synthesis (Abstract deferred^ .. .. .. 398 July. 2. — General Monthly Meeting (Decease of Mr. William Spottiswoode) .. .. .. .. ..399 Nov. 5.— General Monthly Meeting .. .. .. .. 401 Dec. 3. — General Monthly Meeting (Decease of Sir Wm. Siemens) 404 1884. Jau. 18. — Professor Ttndall. — Rainbows .. .. .. 455 „ 25.— H. H. Johnston, Esq. — Kilima-njaro, the Snow-clad Mountain of Equatorial Africa (no Abstract) .. 469 Feb. 1.— Professor F. Max Muller.— Rajah Rammohun Roy, the Religious Reformer of India .. .. 470 „ 4.~ General Monthly Meeting .. .. .. .. 473 CONTENTS. Vll 18S4. Page Feb. 8. — George J. Eomanes, Esq. — The Darwinian Theory of Instinct (Abstract deferred) .. .. .. 476 „ 15. — Professor T. E. Thorpe. — The Chemical Work of Wohler .. ., .. .. .. .. 477 „ 22. — Sir Frederick Bramwell. — London (below bridge) North and South Communication .. ,. 483 Index to Volume X. .. .. .. .. .. .. 608 ( viii ) PLATES. -•<>*- Page Spectrum of Comet, opposite .. .. .. .. .. 4 On Electric Railways .. .. .. .. .. .. 74 Model illustrating Waves .. .. .. .. .. 188 On tlie Ultra-violet Spectra of the Elements (2 Plates) . . 252 103/^ -^«^^ <;^<^ luj I L I B R A R Y . -pi WEEKLY EVENING MEETING,\^\ "^•^ /^ Friday, January 20, 1882. XT^'^ ^V^ George Busk, Esq. F.R.S. Treasurer and Vice-President, in tlieUEalr. William Huggins, Esq. D.C.L. LL.D. F.R.S. On Comets. In the olden time comets were looked upon as the portents of all kinds of woe. In the words of Du Bartas, as rendered by Sylvester* : — " There with louo; bloudy haire, a Blazing Star Threatens the World with Famin, Plague and War : To Princes, death : to Kingdoms, many crosses; To all Estates, ineuitable Losses : To Heard-men, Kot : to Plough-men, hap-lesse Seasons : To Saylers, Storms : to Cities, ciuill Treasons." In the past year, including telescopic comets, no fewer than seven of these blazing stars have threatened us, and certain contemporary events might seem, indeed, to justify this view of their malign influence. But though comets are no longer a terror to us, they are still, in some respects, a great mystery. When we attempt to explain the marvellous phenomeua they present, by the rigid ajjplication of the laws of physics, we find ourselves confronted by prodigious diffi- culties. We are almost led to think that in the heavens, at least, there is more " than is dreamt of in our philosophy " — some profound and still unknown mystery of nature. Not to mention the many absurd theories which are heard on all sides when a great comet appears, on no phenomenon of nature have we so many guesses at truth by the masters of science on different and even ojiposing prin- ciples of explanation. At the present moment there is no consensus of opinion as to the nature of comets. But within the last few years, from two oj)posite directions — from the use of the spectroscope and from mathematical investigation applied to the periodical displays of shooting stars — much knowledge has been gained of their nature, though there are still many points on which we can only speculate. It is my pur^Dose this cveniug to give chief prominence to the new knowledge which these two methods of research have placed within our reach, and to distinguish as clearly as may be possible between what we know about comets and wOiat is not more than speculation. To carry out this purpose we must first study carefully the phe- * Du Bartas, translated by J. Sylvester, fol. 1621, p. 33. Vol. X. (No. 75.) 2 Dr. Huggins [Jan. 20, nomena which have to be explained, namely, the essential appear- ances and changes which comets present during their approach to the sun, at the time that they are visible to us. It is not necessary here to describe in detail the more purely astronomical side of the subject. It will be sufficient to say, in two words, that some comets have become permanent members of our system, while others probably visit us once only, never to return. It depends upon a comet's velocity whether its course shall be a hyper- bola, a parabola, or an ellij)se. In the latter case only can it become a permanently attached member of our system. If the velocity of the comet when at the earth's distance from the sun exceeds 26 miles a second, the comet must go off into space, never to come back to us. If the comet is moving less swiftly its path will return into itself, and it will visit us periodically after longer or shorter wanderings. In the case of many comets, including the brightest comet of last year, their velocity is so near the parabolic limit that it is scarcely possible, from observations made in the small part of their orbit near the sun, to be quite sure whether they will return to us or not. A number of comets, chiefly small ones, arc certainly periodic, and of some comets several returns, true to the calculated time, have been observed. The small portion of the comet's life during which we are able to study it is quite unlike its ordinary humdrum existence. It con- sists of the short period of extreme excitement into which it is thrown by a more or less near approach to the sun — a state of things which is accompanied by rapid and marvellous changes, often on a stupendous scale. The appearances which comets put on under the sun's influence differ widely from each other. A few of these forms, passing from an almost invisible nebulosity up to a brilliant comet of the grand type, are represented on these diagrams. In nearly all these forms three essentially distinctive parts may be seen. 1. The nucleus. With the aid of a telescope, in the heads of most comets a minute bright point may be found. This apparently insig- nificant speck is truly the heart and kernel of the whole thing — poten- tially it is the comet. It is this small part alone which conforms rigorously to the laws of gravitation, and moves strictly in its orbit. If we could see a great comet during its distant wanderings when it has put off the gala trappings of perihelion, it would be a very sober object, and consist of little more than nucleus alone. It is only this part of the comet which can have any claim to solidity, or even appre- ciable weight. Though many of the telescopic comets are of extremely small mass, nucleus included — so small, indeed, that they are unable to perturb such small bodies as Jupiter's satellites — yet in some large comets the nucleus may be a few hundred miles in diameter, and may consist of solid matter. I need not say that the collision of a cometary nucleus of this order with the earth would bo fraught with danger on a very wide scale. 1882.] on Comets, .3 2. The coma. This appears usually as a luminous fog surrounding the nucleus, and gradually shading off from it. The nucleus and the coma form together the head of the comet. 3. The tail. The tail may be considered as a continuation, in a direction opposite to that of the sun, of the luminous fog of the coma. This appendage may be scarcely distinguishable as a slight elongation of the coma, or it may extend half across the heavens, and be many millions of miles in length. The tail may be single, or composed of several branches. We must now study more closely the cometary ap^Dearances as they may be seen when a large telescope is directed to a brilliant comet. I have selected for this jDurpose the Great Comet of 1858, and I shall exhibit on the screen a series of views of this comet, taken at intervals of a few days. The first set shows the growth, position, and forms of the tail, as a whole. The second group represents the more detailed structure and changes of form of the head of the comet, as viewed in a large telescope. These views are, of course, from sketches made at the telescope. Last year several attempts were made to photograph the comet which appeared in June. Mr. Janssen has kindly sent me a positive taken from the original negative. It is now upon the screen. Mr. Janssen purjDosely sacrificed detail in the head of the comet, for the sake of obtaining the structure and form of the tail, exjDOsing the plate for thirty minutes. From a careful examination of several similar negatives, Janssen made a drawing of the comet. A j)hotograph of this drawing is now upon the screen. Mr. Common, at Ealing, with a fine three-foot reflector of his own construction, also photographed the comet, but his object, different from that of Janssen, was to get the form of the nucleus. For this purpose he gave an exposure of only ten minutes — far too short to obtain an impression of the tail. The comet was also photographed by Dr. Draper, of New York. My own work was confined to the comet's spectrum, of which I shall S2)eak presently. We may now advance to the consideration of two primary ques- tions : — 1. Does a comet shine wholly by reflected solar light, or has it also light of its own? 2. Of what materials is a comet composed ? The spectroscope has furnished us with information on both these points. The first successful application of the spectroscope to a comet was in 1864, when Donati discovered in its light three bright bands. In 1866 I was able to distinguish two kinds of light from a telescopic comet — the one kind giving a continuous spectrum and presumably solar light, and the other a spectrum of three bright bands, similar to those which had been seen by Donati. But in 1868 a great advance was made. The close agreement of measures I took of the bands of the comet h of that year with those I had previously taken of the spectrum of certain compounds of carbon led me to compare, directly, in conjunction with my friend Dr. W. Allen Miller, the spectrum of B 2 4 Br. Euggins [Jan. 20, the induction spark in defiant gas with the comet's spectrum, in the manner shown upon the screen. The next diagram shows the result of this direct comparison.* There could be no longer any doubt of the oneness of chemical nature of the cometary stuff with the gas we were using,^ in fact, that carbon, in some form or in some state of combination, existed in the cometary matter. From that time some twenty comets have been examined by different observers. The general close agreement, notwithstanding some small divergencies, of the positions of the three bands with those seen in the flame spectrum of hydrocarbons, leaves no doubt whatever that the original light of comets is really due to matter containing carbon in combination with hydrogen. At first, indeed, for certain reasons, I was led to consider this spectrum to be that of carbon itself in the form of gas, a view still held by some physicists ; but subsequent researches by several experimentalists on this point appear to me to be strongly in favour of carbon combined with hydrogen. f Last year another advance was made. For the first time since the spectroscope has been in the hands of the astronomer the coming of a bright comet made it possible to extend this mode of research into the more refrangible region of the spectrum. Making use of the apparatus and arrangements which I employed for photographing the spectra of stars,| I succeeded in obtaining a photograph of the spectrum of the head of comet h. A copy of this spectrum is now upon the screen (see plate). There is a continuous spectrum which can be traced from about G to beyond K, in which are seen distinctly several of the Fraunhofer lines, G, \ H, K, and many others. The presence of these lines was crucial, and made it certain that this continuous spectrum was really duo to reflected solar light.§ But there was also present a second spectrum consisting chiefly of two groups of brigJd lines. These evidently were due to the same light which is resolved, in the visible region, into the three bright groups. I regarded them with intense interest, for there was certainly hidden within these hieroglyphics some new information for us. Measures of their position in the spectrum, taken under the micro- scope, brought out that these groups were undoubtedly the same * These hydrocarbon groups may be seen with a pocket spectroscope in the blue base of a candle flame or in the flame of a Bunsen burner. t Among many papers, I may refer to * Ueber die Spectra der Cometen,' Dr. Hasselberg, Mem. Acad, des Sciences, St. Pe'tersbourg, vii. ser. tome xxviii. No. 2; and papers by Professors Liveiug and Dewar and by Mr. Lockyer in recent volumes of the ' Proceedings of the Royal Society.' X ' Trans. R. S.' 1880, part 2, p. G71. ' Proceedings R. Instit.' vol. ix. part 3, p. 285. § See observations of the visible spectrum of this comet by Professor Young, the Astronomer Royal, Professor Yogel, Professor Wright, Dr. Von Konkoly, Dr. Hasselberg, and others. Hu^^ ULS Pi-uc.Roy. Inst. Vol.X. CD o CM ^ 5^ Spoliis-f/oodt SiCZzih Zondo-n. 1882.] on Comets. 5 which appear in certain compounds of carbon. Professors Liveing and Dewar had recently shown that these groups indicate a nitrogen compound of carbon, namely, cyanogen. On this view there must be in the cometary matter, besides carbon and hydrogen, the element nitrogen, A few days after my photograph was taken, Dr. Draper succeeded in obtaining a photograph of the comet's spectrum, which appears to confirm mine so far as the bright lines, but does not give the Fraunhofer lines. About the same time that the observations were made on the comet, Professor Dewar succeeded in confirming his results, by the reversal of the groups, employing either titanic cyanide or boron nitride. The positions and characters of these bands, together with those in the visible spectrum, leave no doubt that the substances, carbon, hydro- gen, and nitrogen, and probably oxygen, are present in the cometary matter, and that this light-emitting stuff appears to be essentially of the same chemical nature for all the comets, some twenty, which have been observed up to the present time. Certain minor modi- fications of the common type of spectrum are often present, and show, as was to be expected, that the conditions prevailing in different comets, and indeed in any one comet from day to day, are not rigidly uniform. The temperature, the state of tenuity, the more or less copious supply from the nucleus of the gaseous matter, must be subject to con- tinual variation. At times it is probable that the hydrocarbon spectrum is complicated by traces of the spectrum of the oxygen com- pounds of carbon. These and. other possible variations betray them- selves to us in the spectrum, by the length of range of refrangibility through which each group can be traced, by an alteration in the posi- tion of maximum brightness in the groups, by the relative brightness of the groups, by a more or less breaking up of the shaded light of the bands and the visibility or otherwise of bright lines, by a more or less distinctness of the violet group, and, lastly, by the visibility in the brightest comet of last year of a less refrangible band of the hydrocarbon spectrum which occurs between C and D of the spectrum.* We must now consider the information about the nature of comets which has come to us from a wholly different source. On almost any fine night, after a short watch of the heavens, we shall see the well-known appearances of " shooting stars." At ordinary times, these are small, and appear indifferently in all parts of the heavens, but on certain nights they show themselves in great numbers, and of such brilliancy as to present a spectacle of much magnificence. On such occasions one remarkable feature presents * For these reasons measures of these bands should be considered as strictly applicable to the particular comet at the time of observation only, and not necessarily as applicable to other comets. 6 Br. Huggins [Jan. 20, itself, which is well marked in the diagram on the screen. The meteors all shoot forth from one spot, which is called the radiant point. A little consideration will show that this appearance is really due to perspective, and represents the vanishing point of the parallel courses in which the meteors are moving. Hence we learn that they all belong to an enormous swarm of these bodies which the earth is meeting, and further, we may find the direction in which the swarm is moving relatively to the earth. Now the researches of Olbers, H. A. Newton, and Adams showed that the November shower is really a planetary swarm, revolving round the sun in about 33j years. Further investigations of Schiaparelli, Leverrier, and Oppolzer brought out the astonishing result that the path of the November meteors is really identical with that of a comet discovered by Tempel in 1865. Schiaparelli showed further, that another independent group of meteors which appears in August, has an orbit identical with the third comet of 1862. We are thus led to see the close physical connection, and oneness of origin, if not indeed identity of nature, of comets and of these meteors. Now the meteors on these occasions are too minute to j)ass through the ordeal of ignition by our atmosphere, they are burnt up before they reach the earth, but at other times small celestial masses come down to us, which, there can be little doubt, are of the same order of bodies, and similar in chemical nature. The meteorites we have in our hands, contain matter of the same kind probably as that which gives rise to cometary phenomena. These two small meteorites, which fell at Estherville, were kindly sent to me by Professor Newton, as probably good examples of the sort of stuff of which the nuclei of comets are composed. The question arises, are the revelations of the spectroscope about comets in harmony with what w^e know of the chemical nature of these celestial waifs and strays ? Meteorites may be arranged in a long series, passing from metallic iron alloyed with nickel at one extremity, to those of a stony nature, chiefly silicates, at the other. In meteorites more than twenty of the elementary bodies have been found, including hydrogen, carbon, and nitrogen, which the spectroscope has shown to be in comets. It may be, however, that in the sun's action on comets, we have to do not with the decomposition of the cometary matter, but with the setting free of gases occluded within the meteoric matter, forming the comet's nucleus. If the meteoric matter were decomposed, we should expect a more complicated spectrum. In the year 1867 Professor Odling, lecturing on Professor Graham's researches, lighted up this room with the gas brought by a meteorite from celestial space. This meteorite, of the iron type, yielded nearly three times its volume of gas, of which 85 per cent. was hydrogen, 5 per cent, was carbonic oxide, and 10 per cent, nitrogen. Since that time Professor A. W. Wright has experimented with a meteorite of the stony type, containing, however, numerous very small grains of metallic iron and sulphide of iron scattered 1882.] 071 Comets. 7 through the mass. This meteorite gave off about two and a half times the volume of the meteorite as a whole, or twenty times that of the iron scattered within it. The same gases came off, but in a different proportion ; there being a larger proportion of the oxide of carbon, at a low temperature carbon dioxide was chiefly given off.* Now in all these cases, a spectrum similar to that of comets would be given by these gases under suitable conditions. Some years ago, in conjunction with my friend Professor Maskelyne, I examined the spectra of certain meteorites, and obtained in several cases a spectrum similar to that of comets. Some meteorites like that of Bokkveldt, contain a large percentage of hydrocarbons. Professor Vogel has recently experimented in the same direction, and finds that the gas which comes off from the meteorite he used gives a hydro- carbon spectrum mixed with that of carbonic oxide, and under certain conditions the spectrum of hydrocarbon predominates and becomes almost exactly similar to that of comet h 1881.t We are at a dis- advantage in one particular, for we cannot get at meteorites as they exist in celestial space, but only after superficial ignition in passing through the air. The experiments hitherto made throw but little light on the question, whether cyanogen ready formed is present in combination or otherwise in the comet, or whether it is formed at the time by the interaction of carbonaceous and nitrogenous matter. In the latter case we should have to admit a high temperature, which would be in favour of the view of an electric origin of the comet's light. Professor A. Herschel and Dr. Von Konkoly have pointed out that the spectra of the periodic meteors are different for different groups. I may also mention that Captain Abney considers that he has evidence of hydrocarbons in the outer portion of the sun's atmosphere. » * ' American Journal of Science and Arts,' vol. x. July 1875. t ' Publicationen des Astrophysikulischen Observatoriums,' Band ii. p. 182. Since this Discourse was given, Dr. Flight has presented to the Eoyal Society a paper on the Meteorite of Cranbourne, Australia, and the Eowton Meteoric Iron. In the case of tlie former, the occluded gases amounted to 3*59 the volume of the iron, and consisted of — Carbonic acid 0*12 Carbonic oxide 31 '88 Hydrogen .. 4.5-79 Marsh gas 4 • 55 Nitrogen 17 'GG 100-00 The Eowton Iron gave 6*38 times its bulk of gas, as follows — Carbonic acid 5-155 Hydrogen 77-778 Carbonic oxide 7 ' 345 Nitrogen .. ., .. 9-722 100-000 8 Br. Huggins [Jan. 20' We have now advanced to the extreme boundary of the solid ground of our knowledge of comets. Before us lies the enchanted region of speculation. Without being too venturesome, we may well consider a few points which may explain more in detail some of the phenomena of comets. Of whatever nature we may regard the tremendous changes which take place in them to be, we must certainly look for the primary disturbing couse to the sun. Is the solar heat sufficient to account directly for the self-light of comets, or does it act the part of a trigger, setting free chemical or electrical forces ? On this point of the sufficiency of the solar radiation we must not look to the few cases of excej)tionally close approach to the sun, but to the more average distance of comets at perihelion. Professor Stokes has suggested that some results obtained by Mr. Crookes may throw light upon this question. He concluded from his experiments that in such vacua as exist in planetary space the loss of heat, which in such cases would take place only by radiation, would be exceedingly small.* In this way the heat received from the sun by the comet would accumu- late, and we should get a much higher temperature than would other- wise be j)ossiblc. In this connection may be mentioned the remark- able persistence of the bright trains of meteors in the cold upper air, which sometimes remain visible for three-quarters of an hour before the light fades out by the gradual dissipation of the energy. I need hardly say that the enormous tails of bright comets, many millions of miles in length, cannot be considered as one and the same material object, brandished round like a great flaming sword, as the comet moves about the sun. It is but little less difficult to suppose that the cometary mass is of so large an extent as to include all the sjiace successively occupied by the sweep of the tail at perihelion. On the material theory we seem to be shut up to the view that the tail is con- stantly renewed and reformed, either by matter streaming from the nucleus or in some other way. But this view involves velocities far greater than the force of gravitation can account for. Let us consider the order of the jjhenomena. Under the sun's influence, luminous jets issue from the matter of the nucleus on the side exposed to the sun's heat. These are almost immediately arrested in their motion sun- wards, and form a luminous cap ; the matter of this cap then appears to stream out into the tail, as if by a violent wind setting against it. Now, one hypothesis supposes these appearances to correspond to the real state of things in the comet, and that there exists a repulsive force of some kind acting between the sun and the gaseous matter, after it has been emitted by the nucleus. On this hypothesis the forms of the tails of comets, which are usually curved, and denser on the convex side, admit of explanation. Each particle of matter of the tail must be moving in a curved course, under the influence of the motion it originally possessed, combined with that of this hypothetical repulsive force. But in the form which the tail assumes for us we * I Proceedings R. S.' 1880, p. 248. 1882.] on Comets. 9 have not only to consider the effect of perspective, but also that the comet itself is advancing, so that the visible tail is due to the portion of space which at the time contains all the repelled matter, each particle describing its own independent orbit, and reflecting to the eye the solar light or giving out its own light, as the case may be.* The value of the repulsive force which would be necessary on this theory has been investigated by Bessel, Peirce, and others.f Recently Bredichin J has investigated the curvatures of the tails of a number of comets. According to him, they fall into three classes, which are represented in this diagram, each type of curve depending upon a different assumed value of the repulsive force. This leads to another point, namely, the secondary tails which are often present. Some of these appear to be darted off with an energy of repulsion so enor- * As a rule, the tails of comets appear to be luminous by reflected solar light, but at times the stuff which emits the light giving a spectrum of bright bands is carried into the tail to a greater or less distance from the head, t See numerous papers by Faye in the ' Comptes Kendus.' X ' Annales de rObservatoire de Moscou,' vol. v. liv. 2, p. 30 ; and * Astr. Nachr.'No. 2411. 10 Dr. Hiiggins [Jan. 20, mously great that the original motion of the nucleus tells for very little, and hence the secondary tail is but slightly curved, or even is sensibly straight. Again, if we take the hypothesis that this repulsive force, of whatever character it may be, varies as the surface, and not, like gravity, as the mass, substances of different specific gravity would be differently affected and separated from each other, and these secondary straight, or nearly straight tails would, on this view, consist of the lightest matter. On this hypothesis a comet would suffer of course a large waste of material at each return to perihelion, as the nucleus would be unable to gather up again to itself the scattered matter of the tail ; and this view is in accordance with the fact that no comet of short period has a tail of any considerable magnitude. A theory, based on chemical decomposition, has been proposed by Professor Tyndall,* but as this view has been illustrated here by the eloquent author himself, I will not now enter upon it. A different view of the whole matter has been suggested by Professor Tait.j He supposes, not the nucleus only, but the whole comet, to consist of a swarm, of enormous dimensions, of minute meteoroids, which become self-luminous at and about the nucleus, in consequence of the impacts of the various meteoric masses against each other, giving rise to incandescence, melting, the development of glowing gas, and the crushing and breaking up of the bodies into frag- ments of different sizes, and endowed with a great variety of velocities. The tail he conceives to be a portion of the less dense part of the train illuminated by sunlight, and visible or invisible to us, according not only to circumstances of density, illumination, and nearness, but also of tactic arrangement, as of a flock of birds under different conditions of perspective, or the edge of a cloud of tobacco smoke. On this hypothesis we should expect to find a more comj)licated spectrum, and the spectra of comets to differ greatly from each other. There seems to be a rapidly-growing feeling among physicists that both the self-light of comets and the phenomena of their tails belong to the order of electrical phenomena. One of the most distinguished of the American astronomers wrote to me recently : " As to the American views of the self-light of comets I cannot speak with authority for any one but myself, still I think the prevailing impression amongst us is that the light is due to an electric, or, if I may coin the word electric-oid action of some kind." Here I confess I tread most cautiously, for we have no longer any stepping-stones of fact on which to place our feet. I am ready to admit that the spectroscopic evidence, especially that furnished by the photographs of last year, favours, though it does not necessarily demand, the view that the self-light of comets is due to electric discharges. I do not attach * Phil. Soc. Cambridge, and ' Phil. Mag.' April 1869. t ' Proceedings K. Society Edinburgh,' vol. vi. p. 553. 1882.] on Comets. 11 much importance to the fact that the bright groups in the visible spectrum of comet h agreed with those of the so-called " flame spectrum," for the reason that the same sj)ectrum may be obtained from the induction spark, when suitable arrangements are used to make the discharge one of comparatively low temperature.* As we are now fairly on the wide ocean of speculation, I need not say that the j)recise modes of application of the principle of elec- tricity which have been suggested are many. Broadly, they group themselves about the common idea that great electrical disturbances are set up by the sun's action in connection with the vaporization of some of the matter of the nucleus, and that the tail is matter carried away, possibly in connection with electric discharges, in consequence of the repulsive influence of the sun, which is supposed to be in a state of constant high electrical potential of the same name. Further, it is supposed that the luminous jets and streams and caj)S and envelopes belong to the same order of phenomena as the aurora, the electrical brush, and the stratified discharges of exhausted tubes. Views resting more or less on this basis have been suggested by several physicists, and, in particular, have been elaborated at great length by ZoUner, who endeavours to show that on certain assumed data, which appear to him to be highly probable, the known laws of electricity are fully adequate to the explanation of the phenomena of comets.f All the theories we have considered assume that the bright lines seen in the spectra of comets indicate heated luminous gas. An alternative hypothesis has been suggested by Professor Wright, J and especially by Mr. Johnstone Stoney,§ who considers that the comjDound of carbon vaj)our is opaque in reference to the particular rays which appear as bright lines, and they appear as bright lines in consequence of sending back to us the sun's rays falling upon the vapour. Further, he considers the phenomenon to be of the order of phos- phorescent bodies, and he states that the conditions existing in the cometary gas are such as will eminently promote j)hosphorescence, and therefore visibility, in presence of a luminary. || Here I must stop. May I venture to hoj)e that the experience of the past hour has not been such as to confirm in your minds the old view to which I referred at the beginning of the lecture, that the influence of comets is always a malign and woeful one. [W. H.] * See Professor Piazzi Smyth, ' Nature,' vol. xxiv. p. 430. t • Astr. Nachr.' Nos. 2057-2060, 2082-2086, and ' Ueber die Natur der Cometeu,' Leipzig, 1872. X ' American Journ. S. and A.' vol. x. July 1875. § British Association Report, 1879, p. 251. II Respighi (' Comptes Rendus,' 5 Sept. 1882) has sought indeed to explain the occurrence of bright bands by supposing them to be simply tiie remaining portions of the continuous spectrum of reflected sunlight after absorption through the enormous depth of the comet's atmosphere. This view appears to me for many reasons improbable, especially if we take into account the extreme relative brilliancy of the most refrangible group in the photographic spectrum of comets. 12 Mr. B. S. Poole [Jan. 27, WEEKLY EVENING MEETING, Friday, January 27, 1882. William Bowman, Esq. LL.D. F.R.S. Honorary Secretary and Vice- President, in the Cbair. Reginald Stuart Poole, Esq. of the British Museum, Cor. Inst. France. The Museum and Libraries of Alexandria. The speaker stated that his object was to show the connection between the ancient Egyptian and Alexandrian educational institutions, and expressed his gratitude for the invaluable aid of the eminent French Egyptologist, M. Eevillont. The sources of information are chiefly old hieratic papyri, some of which are actually exercise-books of students, and they tell us of colleges attached to temples in various towns. When Plato and others visited Egypt, Heliopolis was most famous. The subjects taught were religion, law, mathematics, especially geometry and astronomy, medicine and language. There were also primary schools for all classes. Libraries were attached to the temples, and there was a royal library existing at least as early as B.C. 2500. The Alexandrian foundations were due to the wisdom with which the first three Ptolemies carried out the large-minded policy of Alex- ander the Great. They were meant to benefit the mixed population of Alexandria — Egyptian, Greek, and Hebrew. The Museum was a sacred building in the palace, where learned men were maintained by the State to prosecute research. Law and religion were excluded in order to avoid controversy. A botanical garden and a menagerie were added. Besides the similarity of scheme, and the evident succession of Alexandria to Heliopolis, a strong point of contact was the old method, as seen in the mathematical processes of the second Pleron. To the first library, originally Greek only, translations were added, and the temple of Sarapis received surplus books. The first library was burnt when Julius Caesar captured Alexandria. The second, enriched by Antony with the Pergamus collection, is said to have been burnt at the Arab conquest, when it disappeared. The efiect of the Alexandrian foundations was very great. The intelligence of the East and West here met, and it is due to this that the Old Testament was translated into Greek. The Alexandrian University was restored by an Arab Prince, the caliph El-Mutawekkil, two centuries after the conquest; and the 1882.] on the Museum and Libraries of Alexandria, 13 great University of Cairo was founded by a Greek officer of the Fatimite caliph in a.d. 969-70. The University of Cairo practically includes all the Alexandrian faculties except medicine, which is considered by the Arabs to be un- suited to public education. Lately, of 5000 students 2500 were there educated and maintained free of all cost to themselves. The pro- fessors, who now receive moderate rations from the State, make a modest income by outside teaching and copying MSS. WEEKLY EVENING MEETING, Friday, February 3, 1882. William Spottiswoode, Esq. M.A. D.C.L. Pres. R.S. Vice-President in the Chair. Professor Tyndall, D.C.L. F.E.S. M.BJ. Action of Molecules, Free and Constrained, on Hadiant Heat. (Abstract deferred.) 14 General Monthly Meeting. [Feb. 6, GENERAL MONTHLY MEETING, Monday, February 6, 1882. George Busk, Esq. F.R.S. Treasurer and Vice-President, in the Chair. Sidney Biddell, Esq. M.A. The Earl of Dysart, Mrs. Archibald Hamilton, were elected Members of the Royal Institution. Report from the Managers. The following Resolution passed by the Committee of Managers at a Special Meeting held on December 16, 1881, was read and adopted by the Members : — 1. The Board of Managers of the Royal iDstitution received with great regret Mr. Warren De La Rue's letter of December 3, 1881, addressed to Professor Tyndall, announcing that the state of his health compelled him to resign the office of Honorary Secretary to the Royal Institution. 2. The Managers fully ajipreciated the considerate offer made by Mr. De La Rue to continue iu the post of Honorary Secretary for some time longer, if such a course were deemed desirable for the advantage of the Institution; but they believed it to be their duty to secure for Mr. De La Rue the immediate release from the cares of office which seemed indispensable. 3. The Managers trust that Mr. De La Rue may be enabled, after due rest and medical treatment, to resume those scientific pursuits in which so much of his life has been spent, and to the prosecution of which by others so much generous assistance has always been extended by him. 4. The Managers cannot bid farewell to Mr. De La Rue, as Honorary Secretary to the Royal Institution, without tendering to him their warmest thanks for the ability, zeal, and liberality with which he has aided the Royal Institution while filling that important office. 5. The devotion of Mr. De La Rue's time and attention to the interests of the Institution will always be remembered with gratitude in connection with the services of other distinguished men, many of whose names, like his own, belong to the history of science — a history to which the work done in the Royal Institution has made such signal contributions. William Bowman, Esq. LL.D. F.R.S. was elected Honorary Secretary, and Warren De La Rue, Esq. M.A. D.C.L. F.R.S. was elected Manager. Thirteen Candidates for Membership were proposed for election. The Presents received since the last Meeting were laid on the table, and the thanks of the Members returned for the same, viz. : — FROM The Governor General of India — Geological Survey of India : Records. Vol. XIV. Part 4. 8vo. 188L PaliBontologia Indica: Series XIV. Vol. I. Part 3, Fasc. 1. 1882.] General Montlilij Meeting. 15 The Lords Commimoners of the Admiralty— A.cco\\x\i of British Observations of tlie Transit of Venus, Dec. 8, 1874. Edited by Sir G. B. Airy. 4to. 1881. Neiv Zealand Government — Statistics for 1880. fol. 1881. Accademia dei Lincei, Reale, Eoma — Atti, Serie Terza : Vol. VI. Fasc. 2, 3, 4. 4to. 1881. Actuaries, Institute of — Journal. No. 1*24. 8vo. 1881. Asiatic Society of Bengal— J onrnal. Vol. L. Part I. Nos. 3 and 4. Part II. No. 4, 8vo. 1881. Proceedings, No. 9. 8vo. 1881. Asiatic Society, Royal — Journal, New Series, Vol. XIV. Part. 1. 8vo. 1882. Astronomical Society, Royal — Monthly Notices, Vol. XLII. Nos. 1, 2. 8vo. 1881. Ball, Professor R. S. LL.D, F.R.S. (the Author)— A Glimpse through the Ct)rridors of Time. 8vo. 1882. Bankers' Institute— Journal, Vol. II. Part 10. Vol. III. Part 1. Svo. 1881-2. Bartholomeid's Hospital — Statistical Tables for 1880. 8vo. 1881. Batavia Observatory — Eainfall in the East Indian Archipelago, 1880. By P. A. Bergsma, the Director. 8vo. Batavia, 1880. Magnetical and Meteorological Observations, Vol. V. 1879-80. 4to. 1881. Bayley, Francis, Esq. M.R.I. (the Author) — The Bailleuls of Flanders. Svo. 1881. (Privately Printed.) Bramicell, Sir Frederick, F.R.S. M.R.I, (the Author) — Address to the Society of Arts. 8vo. 1881. British Architects, Royal Institute of — Proceedings, 1881-82, Nos. 5, 6, 7, 8. 4to. 1881-2. British Museum Trustees : Cnneiform Inscriptions of Western Asia. Vol. V. Assyria, fol. 1881. Photograph of Shakspere Deed. 1881. Catalogue of Oriental Coins. Vols. IV. V. and VI. Svo. 1879-81. Lepidoptera Heterocera. Parts III. IV. and V. 4to. 1879-81. Catalogue of Birds. Vol. V. Svo. 1881. Catalogue of German and Flemish Prints. Vol. I. Svo. 1879. New Species of Hymenoptera. Svo. 1879. Types of Coleoptera. Part I. Svo. 1879. Catalogue of Persian MSS. Vol. II. 4to. 1881. Hand List of Bibliographies, &c. Svo. 1881. Index of Minerals. Svo. 1881. Chemical Society — Journal for Dec. 1881 and Jan. 1882. Svo. Civil Engineers' Institution — Proceedings, 1881-2. Nos. 2-6. Svo. Conference Polaire Internationale, St. Petersbourg — 3'^ Rapport sur les Actes et Resultats. 4to. 1881. Crisp, Frank, Esq. LL.B. F.L.S. &c.. M.R.I, (the Editor)— J om'ual of the Eoyul Microscopical Society, Series II. Vol. I. Part 6. Svo. 1881. Crookes, W. Odling, W. and C. Meymott Tidy (the Authors) — Reports on London Water Supply, 1880-1. Nos. 10, 11, 12. 4to. Dax: Societe de Borda — Bulletins, 2" Se'rie sixieme Anne: Trimestre 4. Svo. Dax, 1881. East India Associcdion — Journal, Vol. XIII. No. 3. Svo. 1881. Editors — American Journal of Science for Dec. 1881 and Jan. 1882. Svo. Analyst for Dec. 1881 and Jan. 1882. Svo. Athengeum for Dec. 1881 and Jan. 1882. 4to. Chemical News for Dec. 1881 and Jan. 18S2. 4to. Engineer for Dec. 1881 and Jan. 1882. fol. Horological Journal for Dec. 1881 and Jan. 1882. Svo. Iron for Dec. 1881 and Jan. 1882. 4to. Nature for Dec. 1881 and Jan. 1882. 4to. Revue Scientifique and Revue Politique et Litteraire, Dec. 1881 and Jan. 1882, 4to. Telegraphic Journal for Dec. ISSl and Jan. 1882. Svo. Eklund, A. F. Esq. (the Author) — Contribution a la Ge'ographie IMe'dicale. La Nouvelle Caserne des Recrues de Skeppsholm au Point de Vue Hvgic'nique. Svo. Stockholm, 1881. 16 General Monthly Mcding. [Fob. 6, FranJilin Institute— JomnQl, Nos. 672, 673. 8vo. 1881-2. Geographical Society, Eoijal — Pioceedings, New Serks. Vol. III. No. 12. Vol. IV. Nos. 1, 2. 18S1-2. Geological Society— QimvUrly Journal, No. 148. 8vo. 1881. Abstracts of Proceedings, 1881-2, Nos. 408-413. 8vo. Geoloqical Society of Ireland, i?o5 55 55 55 5> At Sea Eiffelberg (8428 ft.) Gornergrat (10,289 ft.) Time. Solar Intensity. Noon 3.30 p.m. Noon 3.15 p.m. Noon 50 P.M. 30 a.m. Noon ,20 a.m. Noon 55 3 P.M. 42 3 \ 34 7 ] 42 1 \ 33 6 1 41 7 ) 33 3 1 33 8 \ 41 7 1 40 9 ) 45 5 i 47 0 1 41 7 / Difference. °C. 7-6 8-5 8-4 7-9 4-6 5-3 Similar testimony is also afforded by a comparison of early and late observations at widely different altitudes : — Variation of Solar Intensity at Different Altitides. Station. Time. Sun's Altitude at Noon. Height above Sea. Solar Intensity. Difference. A.M. o feet. «C. °0 At Sea . . . . 7.35 72 0 28-6 } 8-6 Ri£felberg . . 7.45 60 8428 37-2 At Sea . . . . 8.8 72 • 0 30-3 } 10-6 Eiffelberg . . 8.20 GO 8428 40-9 1882.] on Climate in Toim and Coimtry. 23 The sun's altitude was unfavourable for the comparison ; nevertheless, there were here observed differences of 8' 6 C. and 10-6°. The farther we recede from the earth, the nearer we realise the conditions of solar radiation altogether outside the limits of the atmosj)here, where the solar intensity (assuming the sun's emission to remain constant) is uniform from sunrise to sunset. Throughout the dreary winter days, when, even in the country, a leaden sky opi^resses us, it is tantalising to reflect that, at the moderate height of 5000 feet, which can be reached by a balloon in a few minutes, there is probably blue sky and brilliant sunshine. Latitude profoundly, though irregularly, affects air temperature, for in high latitudes less solar heat falls upon each square foot of the earth's surface, and therefore the air resting upon that surface is warmed to a less extent. But obliquity of the sun's rays has no such influence on solar intensity, for the highest readings of solar heat at or near sea-level have been observed near to the Ai'ctic circle, as is seen from the following table : — Solar Intensity in different Latitudes. Station? Latitude. Sun's Altitude. Sun Temperature. Solar Intensitj'. 0 o OC. °C. At Sea 0 84 78 •9 41-7 Oatlands Park .. 52 N. 61 75 •0 45-0 Isle of Wight .. .. 51 „ 58 72 •3 42-3 At Sea 23 „ 56 71 •7 45-0 Cassel .. 51 „ 53 68 7 Tosten Vierod . . 59 „ 52 73 5 — Whitby 54 „ 50 67 8 36-8 Aak, Eomsdal .. 63 „ 49 82 5 48-7 At Sea 30 „ 48 70 3 43-6 Bellagio 45 „ 47 68-3 39-8 These results show that, with an obliquity of only 6°, the sun temperature and solar intensity were respectively only 78*9° and 41-7° C; whilst, with an obliquity of 41°, they were 82*5° and 48 • 7° C. On the equator at noon, luitli a nearly vertical sun, tlie solar intensity ivas actually 7" C. loiver than in Bomsdal, only 4° S. of the Arctic circle. On the other hand, air-warmth diminishes, as a rule, with increase of latitude, although, as the following table shows there are some remarkable exceptions, for it was 1° higher in lat. 52° N. with an obliouity of 29°, than in lat. 5° N. with an obliquity of only 12°, and in the high latitude 63°, with an obliquity of 41°, it was only 1° C. in arrear of the air-warmth at the equator with an obliquity of only 6°. 24 Br. E. FranJcland [Feb. 10, Shade Temperature at or near Noon and Sea-Level. Station. - Latitude. Sim's Apparent Altitude. Temperature. At Sea, April 10 o 45 S. o 37 18-9 „ March 23 31 58 26 3 „ 22 . 29 60 29 7 >» J5 18 27 65 32 5 ., 17 . 23 68 32 8 )♦ v 16 20 71 29 4 »» »> -lii 11 82 37 2 M 5> I'" 10 83 37 2 „ 11 . 9 85 36 5 »> »> 6 . 0 84 37 2 j» » 4 . 3N. 81 30 0 »> » ^ • 5 ) 78 29 4 ») M 2 , 8 , » 75 31 7 „ Feb. 24 . 17 >) 64 28 0 „ 20 . 21 J 58 28 3 » >i 19 23 1 5G 27 2 » >, 16 30 ) 48 28 9 „ Jan. 27 51 , » 21 10 6 Bellagio, Sept. 17 . 45 > 47 28 5 Oatlands Park, June 8 52 , 1 61 30 0 Isle of Wight, May 13 51 ; ) 57 28 9 >» » )> 14 51 , ) 58 29 0 H 5» 5} ■*" 51 , 5 58 30 0 Whitby, Aug. 16 54 , 9 50 32 2 Aak, Romsdal, July 15 63 , 5 49 3G-2 Shortly summarised, therefore , the conditions most favourable for a genial climate — Depending on solar intensity, are — Depending on air temperature, are — 1. Great elevation above sea-level. 1. Slight elevation above sea-level. 2. A light-coloured ground and back- 2. A dark-coloured ground and back- ground. ground. 3. Shelter. Keception of direct and 3. Shelter. Reception of direct and reflected rays. reflected rays. 4. A clear sun with white clouds. 4. A clear sun with white clouds. 5, A clean atmosphere. No dust, 5. A clean atmosphere. No dust. smoke, or fog. smoke, or fog. 6. A minimum of watery vapour in 6. A maximum of watery vapour in the air. the air. Thus whilst there are three conditions common to both categories, the three remaining ones are diametrically opposed to each other. Town Climate. The climate of towns depends upon the same essential conditions as that of the country, but some of these are more within our own control in towns. The great evils of our town climate are excessive heat in summer 1882.] on Climate in Town and Country. 25 and cheerless gloom in winter. We suffer less, however, from exces- sive solar intensity than continental cities between the same parallels of latitude, owing to the very causes which plunge us into a more miserable gloom in winter. Light-coloured walls neither make our streets look cheerful nor feel hot. Such sad colours as brick, stone, stucco, or paint give to our houses are soon changed to a grimy neutral tint, powerless to reflect either solar light or heat. The darker the colour of the houses, the cooler the streets and the hotter the rooms during sunshine, and vice versa. Whilst the summer climate in our streets and houses is thus, to a considerable extent controllable, that of winter, which depends so much on a clean atmosphere, is still more so. All our towns are nearly at the sea- level, a position favourable for air-, but not for sun- warmth. In our large towns, however, we artificially create an impenetrable barrier to solar radiation by throwing into the air the imperfectly burnt products of bituminous coal. These products are of three kinds — soot, tar and steam. Every ton of bituminous coal burnt in our grates gives off about 6 cwts. of volatile but condensable products. The less perfect the combus- tion the more tar and the less steam will be produced. If perfectly burnt without any smoke, then about 9 cwts. of steam, occupying 27,359 cubic feet at 100° C, or 20,024 cubic feet at 0° C. will be sent into the air. Now 33,333 tons of bituminous coal are, on the average, daily consumed in London in winter, giving 667,460,000 cubic feet of steam at 0° C. This combustion of enormous quantities of bituminous coal acts in the production of town fog in three ways : — 1st. By supplying the basis of all fog — condensed watery particles. 2nd. By determining the condensation of atmospheric moisture in the form of fog. 3rd. By coating the fog particles with tar, and thus making them more persistent. All fogs have for their basis watery particles, and the greater part even of the suspended matters visible in a ray of electric light consists of these particles, for the air becomes nearly clear when it is heated somewhat above 100° C. [Experiment shown]. Everything therefore which increases the proportion of aqueous vapour in town air tends to produce fog. But aqueous vapour alone would probably never produce fog, for it condenses at once to large particles, which rapidly fall as rain. When, however, solid or liquid particles are present in the air, the minute spherules of fog are produced. This was first shown by Messrs. Coulier and Mascart, in 1875, and their results have since been confirmed by Mr. Aitkin. The speaker showed that air filtered through cotton wool, though afterwards saturated with moisture, produced no fog when its temperature was lowered ; but as soon as a small quantity of the dusty air of the theatre was admitted fog was immediately formed, whilst, when a little coal smoke was introduced, a dense and more persistent fog was the result. 26 Dr. E. FranJcland [Feb. 10, The fog once formed is rendered more persistent by tlie coating of tarry matter wbich it receives from the products of the imperfect combustion of smoky coal. The speaker had made numerous experiments on the retardation of evaporation by films of coal tar. He had found that the evaporation of water in a platinum dish placed in a strong draught of air was retarded in one experiment by 84 per cent, and in another by 78*6 per cent., when a thin film of coal tar was placed on the surfaces. Even by the mere blowing of coal smoke on the surface of the water for a few seconds, the evaporation was retarded by from 77*3 to 81*5 per cent. Drops of water suspended in loops of j)latinum wire were also found to have their evaporation retarded by coal smoke. Hence arise the so-called dry fogs which have been observed by Mr. Glaisher in balloon ascents, some examples of which are given in the following table : — Foa IN COMPARATIVELY DrY AiR. Place of Ascent. Altitude. Wolverhampton . . Crystal Palace . . >» Woivertou Woolwich 5» foot. 5,922 3,698 9,000 1,000 11,000 6,000 4,400 Temperature of Air. ° F. 53-5 385 32-5 64-7 30-0 44-0 42-0 Degree of Huuiidity. 100 =: Saturation. 61 62 52 53 68 64 52 Thus the smoke of our domestic fires constitutes a potent cause both for the generation and the persistency of town fogs. In London, at all events, if all manufacturing oj^erations were absolutely to cease, the fogs would not be perceptibly less dense or irritating. Granting then this cause of town fogs, what are the remedies open to us ? The speaker was of opinion that the substitution of a suffi- cient number of smoke-consuming grates (assuming a smoke-con- suming grate to have been invented), for the 1,800,000 fire-places of London was quite hopeless, and that one remedy only could be of any appreciable service — tlie importation of bituminous coal must he forhidden. This is a case in which individual efi'ort can do nothing ; but State or municipal action would be simple and decisive. There need be no fear that the price of smokeless fuel would rise inordinately, for the sources of this fuel are too numerous and inex- haustible to admit of either a monopoly or a serious rise in price. In addition to the enormous stores of smokeless coal in the Welsh coal- fields, every bituminous coal yields a smokeless coke, either in the retorts of gasworks or in coke ovens. On the average, 100 tons of smoky coal yield 60 tons of coke, the remaining 40 tons being driven off as combustible'^'gas, ammoniacal liquor and tar ; and as there is an almost unlimited demand for these products, it is not 1882.] on Climate in Town and Countrij. 27 unlikely that they would, under the circumstances contemplated, repay the cost of coking, and it is worthy of note that coal of very inferior quality makes fairly good coke. The only objection to the domestic use of smokeless coal and coke is the difficulty of lighting the fire, but this is obviated by the use of gas as proposed by Dr. Siemens. In ordinary grates, however, there is little difficulty in lighting and burning these smokeless fuels if the throat of the chimney be contracted so as to increase the draught. In this way nearly every grate in London could be rendered smokeless at an expenditure of a couple of shillings. It is unnecessary to enumerate the many advantages of a smoke- less atmosphere, but it may here be mentioned that London fogs not only seriously injure health but annually destroy the lives of thou- sands. In one week alone upwards of 1100 lives have been thus sacrificed in London. We have doubtless still long to wait before the only remedy for London fogs will be adopted ; but in the mean- time, immunity from their effects, so far as the respiratory organs are concerned, may be obtained by the use of a small and very portable cotton- wool respirator which is made, in accordance with the speaker's directions, by Mr. Casella, of Holborn. [Eespirator exhibited.] Armed with this little instrument, he had often passed through the densest and most irritating fogs with perfect immunity, breathing, in fact, all the time, air even purer than that of the country. Such a remedy is, however, obviously of extremely limited application. In conclusion he said, though we may, with justice, complain of the scanty share of sunshine now received by us, let us not forget that, in our coal-fields, we are compensated by vast stores of the sunlight of past ages. How far, through electricity, these stores can be evoked to supplement the present defective supply, he would be a bold man who would venture to predict. Let us not, however, con- tinue to use this great legacy of light of the past to obscure the small one of the present. [E. F.] WEEKLY EVENING MEETING, Friday, February 17, 1882. Sir Frederick Bramwell, F.E.S. Vice-President, in the Chair. Professor John G. McKendrick, M.D. F.R.S.E. Tlie Breathing of Fishes. y^^- (Abstract deferred.) /O^^/o 28 Sir B. C. Brodies Besearches on Chemical Allotropy. [Feb. 24, WEEKLY EVENING MEETING, Friday, February 24, 1882. SiE Fredekick Bramwell, F.E.S. Vice-President, in the Chair. Professor Odling, M.A. F.E.S. M.B.I. Sir B. C. Brodie's Besearches on Chemical Allotropy. (Abstract deferred.) ^ 1882.J Mr. Alfred Taylor on Homan Antiquities, &c. ^ 29 WEEKLY EVENING MEETING, Friday, March 3, 1882. William Bowman, Esq. LL.D. F.R.S. Honorary Secretary and Vice-President, in the Cliair. Alfred Ttlob, Esq. F.G.S. M.B.L Moman Antiquities recently found in London, The speaker began by referring to some Eoman remains discovered near Warwick Square, E.G. London, last year, about nineteen feet below the present surface ; and with remarks on a series of diagrams illus- trating the history of Roman London, and its site, boundaries, walls, and streets, and the principal roads issuing from it to other parts of the island. Many specimens of the relics discovered and large drawings of others were exhibited. They will go to the British Museum, on loan. The collection includes several cinerary urns, containing tha results of the cremation of human bodies. One urn, fifteen inches high, was of glass. A remarkable turned vase of stone was found. Four of the urns were inclosed in leaden ossuariae, made without solder ; some of the remainder were protected by roofing tiles. On the inside of one ossuarium was an emblem of Mithra, the Persian sun-god. The lecturer explained its difference from the emblem chosen by the Emperor Constantino. It differs from the early Christian labarum in being an eight-rayed cross without the R. In reference to the ossuariae, Mr. Tylor said that the arts of smelt- ing and working lead were practised and probably invented in this country in very ancient times ; and that at Avignon and Lyons he saw Roman lead-work, bearing the inscription " Cantius," i. e. " a Kentish- man." Another British word, Cimobarrus, was found on lead-work at Caistor near Peterboro'. This specimen is now in the British Museum. ^ The coins found during Mr. Tylor's excavations were dated from A.D. 46 to 300. The date of the Mithraic emblem was considered to be soon after a.d. 50, much earlier than that on the Portland Vase. Suggestive remarks were made on the probably advanced stage of civilisation in Britain at the time of the Roman invasion indicated by the statements of contemporary historians and other sources. In conclusion, Mr. Tylor stated that the greatest care had been taken to lay down the exact position of each article found, on a plan, and that this would be published in the ' Archselogia ' shortly. 30 General Monthly Meeting. [March 6, GENERAL MONTHLY MEETING, Monday, March G, 1882. George Busk, Esq. F.R.S. Treasurer and Vice-President, in the Chair. Walter H. Coffin, Esq. F.L.S. F.C.S. Andrew Ainslie Common, Esq. F.E.A.S. Duncan Darroch, Esq. Captain Montagu Dettmar, Francis Y. Edgeworth, Esq. M.A. Mrs. John Macnaught, Vice- Admiral Frederick Augustus Maxse, M. de Meritens, Wilson Noble, Esq. M.A. George William Stevens, Esq. Frederick Purdy, Esq. F.S.S. Frederick Kamadge, Esq. Mrs. George J. Eomanes, were elected Members of the Eoyal Institution. The Special Thanks of the Members were returned to M. Janssen for his Photographs of the Sun. The Chairman reported that he had received the following Letter from Mr. Warren De La Rue : — " 73, Portland Place, W. « Dear Mr. Busk, February 7, 1882. " I am deeply sensible of the indulgent appreciation of my services as Secretary of the Royal Institution, expressed in the Resolution of the Committee of Managers on December 16th, 1881, and adopted by the General Meeting of Members yesterday. " The kind and sympathetic feeling which pervades the elegantly expressed document, in which the sentiments of the Managers are embodied, is most gratifying to me and my family. " On my part I can assure you that no post I have ever held has been pro- ductive of so much satisfaction and pleasure as that which I most reluctantly resigned on account of failing health. " To the Royal Institution I owe a debt of deep gratitude for the help I have received in and the impulse it has given to my scientific work, from tlie time, now far distant, when Faraday first conferred on me the boon of a Friday Evening card. " My interest in the Royal Institution will never cease. " Yours sincerelv, "Warren De La Rue." 1882.] General MontUij Meeting. 31 The following arrangemeuts for the Lectures after Easter were announced : — Edward B. Tylok, Esq. D.C.L. F.R.S. — Four Lectures ou The History op Customs and Beliefs; on Tuesdays, April 18 to May 9. Professor Arthur Gamgee, M.D. F.R.S. — Four Lectures on Digestion ; on Tuesdays, May 16 to June 6. Professor Dewar, M.A. F.R.S. — Eight Lectures on The Chemical and Physical Properties of the Metals ; on Thursdays, April 20 to June 8. Frederick Pollock, Esq. M.A. — Four Lectures on The History of the Science of Politics; on Saturdays, April 22 to May 13. David Masson, Esq. LL.D. F.R.S.E. Professor of Rhetoric and English Literature, University of Edinburgh. — Four Lectures on Poetry and it3 Literary Forms ; on Saturdays, May 20 to June 10. The Presents received since the last Meeting were laid on the table, and the thanks of the Members returned for the same, viz. : — FROM Secretary of State for India — Report on Publjc Instruction in Bengal, 1880-1. fol. 1881. Accademia dei Lincei, Reale, Roma — Atti, Serie Terza : Vol. VI. Fasc. 6. 4to. 1882. Astronomical Society, Eoyal— Monthly Notices, Vol. XLII. No. 3. 8vo. 1882. Memoirs, Vol. XLVI. 18S0-1. 4to. 1881. BanTxers' Institute— Jomnsil, Vol. III. Part 2. 8vo. 1882, Bavarian Academy of Sciences, Boyal — Sitzungsberichte : 1882, Heft 1. 8vo. British Architects, Roval Institute o/— Proceedings, 1881-2, Nos. 9, 10. 4to. 1881-2. British Museum Trustees— Catalogue of Spanish MSS. By P. de Gazangos. Vol. III. 8vo. 1881. Chemical Society— Jomneil for Feb. 1882. 8vo, Civil Engineers' Institution — Proceedings, 1881-2. 8vo. Nos, 7-9. Crisjy, Frank, Esq. LL.B. F.L.S. &c. MR.I. {the Editor)— Souxnol of the Royal Microscopical Society, Series II. Vol. II. Part 1. 8vo. 1882. Croohes, W. Odlincj, W. and C. Meymott Tidy {the Authors)— Bepoita on London Water Supply, No. 13. 4to. 1882. Editors — American Journal of Science for Feb. 1882. 8vo. Analvst for Feb. 1882. 8vo. Athenaeum for Feb. 1882. 4to. Chemical News for Feb. 1882. 4to. Engineer for Feb, 1882. fl. Horological Journal for Feb. 1882. 8vo. Iron for Feb. 1882. 4to. Nature for Feb. 1882. 4to. Revue Scientifique and Revue Politique et Litte'raire for Feb. 1882. 4to. Telegraphic Journal for Feb. 1882. fol. Franklin Institute— J omnal. No. 674. 8vo. 1882. Geogrcqjhical Society, Royal — Proceedings, New Series, Vol. IV. No. 8. 8vo. 1882. Geological Institute, Imperial, Vienna — Verhandlungen, 1881, Nos. 1-18. 8vo. Jalirbuch : Band XXXI. No. 4. 8vo. 1881. Geological Society — Quarterly Journal, No. 149. 8vo. 1882. Abstracts of Proceedings,'l8Sl-2, Nos. 414-416. 8vo. Grey, Henry, Esq. (the Author) — The Classics for the Million: an Epitome, in Englisli, of the Works of Greek and Latin Authors. 12mo. 1881. Lisbon, Sociedade de Geographia — Boletim, 2* Serie, Nos. 7 and 8. 8vo. 1881. 32 General MontJdy Meeting. [March 6, Manchester Geological Society — Transactions, Vol. XVI. Parts 11, 12. 8vo. 1881. Meteorological Office — Communications from the International Polar Commission. Part 1. 4to. St. Petersburg, 1882. Miller, W. J. C. Esq. B.A. (the Eegistrar)— The Medical Kegister. 8vo. 1882. The Dentist's Register. 8vo. 1882. Pharmaceutical Society of Great Britain — Journal, Feb. 1882. 8vo. Calendar, 1882. 8vo. 1882. Photoqraphic Society — Journal, New Series, Vol. VI. No. 5. 8vo. 1882. Pole, 'William, Esq. F.E.S. M.InstC.E. (the Author)— A. Study of the Problem of Aerial Navigation. (Min. of Proc. of Inst, of Civil Eng. vol. 67.) 8vo. 1882. Preussische Ahademie der Wissenschaften — Monatsberichte : Dec. 1881. 8vo. Boyal Dublin Society — Scientific Transactions, Vol. I. (Series II.) Parts 13, 14. 4to. 1880-1. Scientific Proceedings, Vol. II. (New Series) Part 7. Vol. III. Parts 1-4. 8vo. 1880-1. Royal Society of London — Proceedings, No. 217. 8vo. 1882. Society of Arts — Journal, Feb. 1882. 8vo. Statham, H. H. Esq. (the Author) — Notes on Ornament. (Lectures delivered at the Royal Institution.) (Portfolio, Feb. 1882.) St. Barfholomeio's Hospital — Reports, Vol. XVII. 8vo. 1881. St. Petersbourg, Akademie des Sciences— Mevaoires, 7® Serie, Tome XXIX. No. 2. 4to. 1881. Bulletins, Tome XXVII. No. 4. 4to. 1881. Symons, G. J. — Monthly Meteorological Magazine, Feb. 1882. 8vo. Telegraph Engineers, Society of — Vol. X. No. 39. 8vo. 1882. Teyler Museum — Archives: Serie II. 2^ Partie. 4to. 1881. Origine et but de la Fondation Teyler. Par E. van der Ven. 4to. 1881. ToMo University — Memoirs, Nos. 4, 5. 4to. 1881. Verein zur Beforderung des Gewerbfleisses in Preussen — Verhandlungen, 1882: No. 1. 4to. 1882.] Mr. Swan on Electric Lighting hij Incandescence. 33 WEEKLY EVENING MEETING, Friday, March 10, 1882. Sir Frederick Bramwell, F.R.S. Vice-President, in the Chair. Joseph W. Swan, Esq. Electric Lighting hy Incandescence. Speaking in this place on electric light, I can neither forget, nor for- bear to mention, as insej)arably associated with the subject and with the Royal Institution, the familiar, illustrious, names of Davy and Faraday. It was in connection with this Institution that, eighty years ago, the first electric light experiments were made by Davy, and it was also in connection with this Institution that, forty years later, the foundations of the methods, by means of which electric lighting has been made useful, were strongly laid by Faraday. I do not propose to describe at any length the method of Davy. I must, however, describe it slightly, if only to make clear the differ- ence between it and the newer method which I wish more particularly to bring under your notice. The method of Davy consists, as almost all of you know, in pro- ducing electrically a stream of white-hot gas between two pieces of carbon. "When electric light is produced in this manner, the conditions, which surround the process are such as render it impossible to obtain a small light with proportionally small expenditure of power. In order to sustain the arc in a state approaching stability, a high electro-motive force and a strong current are necessary ; in fact, such electro-motive force and such current as correspond to the jDroduction of a luminous centre of at least several hundred candle-power. When an attempt is made to produce a smaller centre of light by the em- ployment of a proportionally small amount of electrical energy, the mechanical difiiculties of maintaining a stable arc, and the diminution in the amount of light (far beyond the diminished power employed), put a stop to reduction at a point at which much too large a light is produced for common purposes. The often-repeated question, " Will electricity supersede gas?" could be promptly answered if we were confined to this method of producing electric light ; and for the simple reason that it is im- possible, by this method, to produce individual lights of moderate power. The electric arc does very well for street lighting, as you all know from what is to be seen in the City. It also does very well for Vol. X. (No. 75.) d 34 Mr. JosejiJi W. Sican [March 10, the illninination of such large enclosed spaces as railway stations; but it is totally unsuited for domestic lishtincr, and for nine-tenths of the other purposes for which artificial light is required. If electricity is to compete successfully with gas in the general field of artificial lighting, it is necessary to find some other means of obtaining light through its agency than that with which we have hitherto been familiar. Oui* hope centres in the method — I will not say. the new method — but the method -which until within the last few years has not been applied with entire success, but which, within a recent period, has been rendered perfectly practicable — I mean the method of producing light hy electrical incandescence. The fate of electricity as an agent for the production of artificial light in substitution for gas, depends greatly on the success or non- success of this method ; for it is the only one yet discovered which adapts itself with anything like completeness to all the pm'poses for which artificial lighting is required. If we are able to produce light economically through the mediimi of electrical incandescence, in small quantities, or in large quantities, as it may be required, and at a cost not exceediug the cost of the same amount of gas light, then there can be little doubt — there can, I think, be no doubt — that in such a form, electric light has a great future before it. I propose, therefore, to explain the principle of this method of lighting hy incandescence^ to show how it can he applied, and to discuss the question of its cost. When an electrical current traverses a conducting wire, a certain amount of resistance is opposed to the passage of the current. One of the eftects of this conflict of forces is the development of heat. The amount of heat so developed depends on the nature of the wire — on its length and thickness, and on the strength of the current which it carries. If the wire be thin and the current stronsr, the heat developed in it may be so great as to raise it to a white heat. The experiment I have just shown, illustrates the principle of Electric Lighting by Incandescence, which is briefly this — that a state of white heat may he produced in a continuous solid conductor hy passing a su^ciently strong electrical current through it. A principle, the importance of which cannot well be overestimated, underlies this method of producing light electrically — namely, the principle of divisibility. By means of electric incandescence it is possible to produce exceedingly small centres of light, even so small as the light of a single candle ; and with no greater expenditure of power, in proportion to the light produced, than is involved in the maintenance of light-centres 10 or 100 times greater. Given a cer- tain kind of wire, for example a platinum wii-e, the 100th of an inch in diameter, a certain quantity of current would make this wire white- hot whatever its length. If in one case the wire were one inch long and in another case ten inches long, the same current passing through these two pieces of similar wire, would heat both to precisely the same temperature. But in order to force the same current thi'ough 1882.] on Electric Lighting by Incandescence. 35 the ten times longer piece, ten times the electro-motive force or, if I may be allowed the expression, electrical pressnre, is required, and exactly ten times the amount of energy would be expended in pro- ducing this increased electro-motive force. Considering, therefore, the proportion between power applied and light produced, there is neither gain nor loss in heating these dinerent lengths of wire. In the case of the longer wire, as it had ten times the extent of surface, ten times more light was radiated from it than from the shorter wire, and that is exactly equivalent to the propor- tional amount of power absorbed. It is therefore evident that wltether a short piece of wire or a long piece is electrically heated, the amount of light produced is exactly proportional to the power expended in producing it. This is extremely important ; for not only does it make it possible to produce a small light where a small light is required, without having to pay for it at a higher rate than for a larger light, but it gives also the great advantage of obtaining equal distribution of light. As the illuminating effect of light is inversely as the square of the distance of its source, it follows that where a large space is to be lighted, if the lighting is accomplished by means of centres of light of great power, a much larger total quantity of light has to be employed, in order to make the spaces remotest from these centres sufficiently light, than would be required if the illumination of the space were obtiiined by numerous smaller lights equally distributed. In order to practically apply the principle of producing light by the incandescence of an electricallv heated continuous solid conductor, it is necessary to select for the light-giving body a material which offers a considerable resistance to the passage of the electric current, and which is also capable of bearing an exceedingly high temperature without undergoing fusion or other change. As an illustration of the difference that exists amoncr different substances in respect of resistance to the flow of an electric current, and consequent tendency to become heated in the act of electrical transmission, here is a wire formed in alternate sections of platinum and silver ; the wire is perfectly uniform in diameter, and when I pass an electric current through it, although the current is uniform in every part, yet, as you see, the wire is not uniformly hot, but white- hot only in parts. The white-hot sections are platinum, the dark sections are silver. Platinum offers a hisher decrree of resistance to the passage of the electric current than silver, and in consequence of this, more heat is developed in the platinum than in the silver sections. The high electrical resistance of platinum, and its high melting- point, mark it out as one of the most likely of the metals to be useful in the construction of incandescent lamps. When platinum is mixed with 10 or 20 per cent, of iridium, an alloy is formed, which has a much higher melting-point than platinum ^ and many attempts have been made to employ this alloy in electric lamps. But these attempts have not been successful, chiefly because high as is the melting-point r 2 36 Mr. Joseph W. Swan [March 10, of iridio-platinum, it is not liigli enough to allow of its being heated to a degree that woukl yield a sufficiently large return in light for energy expended. Before an economical temperature is reached, iridio-platinum wire slowly volatilises and breaks. This is a fatal fault, because in obtaining liglit by incandescence there is the greatest imaginable advantage in being able to heat the incandescing body to an extremely high temperature. I will illustrate this by experiment. Here is a glass bulb containing a filament of carbon. When I pass through the filament one unit of current, light equal to two candles is produced. If now I increase the current by one half, making it 07ie unit and a half, the light is increased to thirty candles, or thereabout, so that for this one half increase of current (which involves nearly a doubling of the energy expended), fifteen times more light is j)roduced. It will readily be understood from what I have shown that it is essential to economy that the incandescing material should be able to bear an enormous temperature without fusion. We know of no metal that fulfils this requirement ; but there is a non-metallic substance which does so in an eminent degree, and which also possesses another necessary quality, that of loio conductivity. The substance is carbon. In attempting to utilise carbon for the purpose in question, there are several serious practical difficulties to be overcome. There is, in the first place, the mechanical difficulty arising from its intract- ability. Carbon, as we commonly know it, is a brittle and non-elastic substance, possessing neither ductility nor plasticity to favour its being shaped suitably for use in an electric lamp. Yet, in order to render it serviceable for this purpose, it is necessary to form it into a slender filament, which must possess sufficient strength and elasticity to allow of its being firmly attached to conducting wires, and to prevent its breaking. If heated white hot in the air, carbon burns away ; and therefore means must be found for preventing its com- bustion. It must either be placed in an atmosphere of some inert gas or in a vacuum. During the last forty years, spasmodic efibrts have from time to time been made to grapple with the many difficulties which surround the use of carbon as the wick of an electric lamp. It is only within the last three or four years that these difficulties can be said to have been surmounted. It is now found that carbon can be produced in the form of straight or bent filaments of extreme thinness, and possessing a great degree of elasticity and strength. Such filaments can be produced in various ways — by the carbonisation of paper, thread, and fibrous woods and grasses. Excellent carbon filaments can be produced from the bamboo, and also from cotton thread treated with sulphuric acid. The sulphuric acid treatment efiects a change in the cotton thread similar to that which is effected in paper in the process of making parchment paper. In carbonising these materials, it is of course necessary to preserve them from contact with the air. This is done by surrounding them with charcoal. 1882.] on Electric Lighting hij Incandescence. 37 Here is an example of a carbon filament produced from parch- mentised cotton thread. The filament is not more than the '01 of an inch in diameter, and yet a length of three inches, having therefore a surface of nearly the one-tenth of an inch, gives a light of twenty candles when made incandescent to a moderate degree. I have said, that, in order to preserve these slender carbon filaraents from combustion, they must be placed in a vacuum ; and experience has shown that if the filaments are to be durable, the vacuum must be exceptionally good. One of the chief causes of failure of the earlier attempts to utilise the incandescence of carbon, was the imperfection of the vacua in which the white-hot filaments were placed ; and the success which has recently been obtained is in great measure due to the production of a better vacuum in the lamps. In the primitive lamps, the glass shade or globe which enclosed the carbon filament w^as large, and usually had screw joints, with leather or indiarubber washers. The vacuum was made either by filling the lamp with mercury, and then running the mercury out so as to leave a vacuum like that at the upper end of a barometer, or the air was exhausted by a common air pump. The invention of the mercury pump by Dr. Sprengel, and the publication of the delicate and beautiful experiments of Mr. Crookes in connection with the radio- meter, revealed the conditions under which a really high vacuum could be produced, and in fact gave quite a new meaning to the word vacuum. It was evident that the old incandescent lamp experiments had not been made under suitable conditions as to vacuum ; and that before condemning the use of carbon, its durability in a really high vacuum required still to be tested. This idea having occurred to me, I com- municated it to Mr. Stearn, who was working on the subject of high vacua, and asked his co-operation in a course of experiments having for their object to ascertain whether a carbon filament produced by the carbonisation of paper, and made incandescent in a high vacuum was durable. After much experimenting we arrived at the conclusion that ivhen a loell-formed carbon filament is firmly connected ivith con- ducting wires, and placed in a hermetically sealed glass hall, perfectly exhausted, the filament suffers no apparent change even, ichen heated to an extreme degree of tvhiteness. This result was reached in 1878. It has since then become clearly evident that Mr. Edison had the same idea and reached the same conclusion as Mr. Stearn and myself. A necessary condition of the higher vacuum was the simplification of the lamp. In its construction there must be as little as possible of any material, and there must be none of such material as could occlude gas, which being eventually given out would spoil the vacuum. There must besides be no joints except those made by the glass-blower. Therefore, naturally and per force of circumstances, the incan- descent carbon lamp took the most elementary form, resolving itself into a simple hulh, pierced hy two platinum wires supporting a filament of carbon. Probably the first lamp, having this elementary character, ever publicly exhibited, was shown in operation at a meeting of the 38 Mr. Joseph W. Swan [March 10, Literary and Pliilosophical Society of Newcastle in February, 1879. The vacuum had been produced by Mr. Stearn by means of an im- proved Sprengel pump of his invention. BLickening of the lamp glass, and speedy breaking of the carbons, had been such invariable accompaniments of the old conditions of imperfect vacua, and of imperfect contact between carbon and con- ducting wires, as to have led to the conclusion that the carbon was volatilised. But under the new conditions these faults entirely dis- appeared ; and carefully conducted experiments have shown that well- made lamps are quite serviceable after more than a thousand hours' continual use. Here are some specimens of the latest and most perfected forms of lamp. The mode of attaching the filament to the conducting wires by means of a tiny tube of platinum, and also the improved form of the lamp, are due to the skill of Mr. Gimmingham. The lamp is easily attached and detached from the socket which connects it with the conducting wires ; and can be adapted to a great variety of fittings, and these may be provided with switches or taps for lighting or extinguishing the lamps. I have here a lamp fitted especially for use in mines. The current may be supj^lied either through main wires from a dynamo-electrical machine, with flexible branch wires to the lamp, or it may be fed by a set of portable store cells closely connected with it. I will give you an illustration of the qualify of the light these incandescent lamps are capable of producing by turning the current from a Siemens' dynamo-electric machine (which is working by means of a gas engine in the basement of the building) through sixty lamps ranged round the front of the gallery and through six on the table. (The theatre was now completely illuminated by means of the lamps, the gas being turned off during the rest of the lecture.) It is evident by the appearance of the flowers on the table that colours are seen very truly by this light, and this is suggestive of its suitability for the lighting of pictures. The heat produced is comparatively very small ; and of course there are no noxious vapours. And now I may, I think, fairly say that the difficulties encountered in the construction of incandescent electric lamps have been com- pletely conquered, and that their use is economically practicable. In making this statement I mean, that, both as regards the cost of the lamp itself and the cost of supplying electricity to illimmiate it, light can be produced at a cost which will compare not unfavourably with the cost of gas light. It is evident that if this opinion can be sus- tained, lighting by electricity at once assumes a position of the widest public interest, and of the greatest economic importance ; and in view of this, I may be permitted to enter with some detail into a considera- tion of the facts which support it. There has now been sufficient experience in the manufacture of lamps to leave no doubt that they can be cheaply constructed, and wo 1882.] on Electric Ligliting hij Incandescence. 39 know by actual experiment that continuous heating to a fairly high degree of incandescence during 1200 hours does not destroy a well- made lamp. What the utmost limit of a lamp's life may be, we really do not know. Probably it will be an ever-increasing span ; as, wdth increasing experience, processes of manufacture are sure to become more and more perfect. Taking it, therefore, as fully esta- blished that a cheap and durable lamp can now be made, the further question is as to the cost of the means of its illumination. This question in its simplest form is that of the more or less economical use of coal; for coal is the principal raw material alike in the production of gas and of electric light. In the one case, the coal is consumed in producing gas which is burnt ; in the other in pro- ducing motive power, and, by its means, electricity. The cost of producing light by means of electric incandescence may be compared with the cost of producing gas light in this way, — 2 cwt. of coal produces 1000 cubic feet of gas, and this quantity of gas, of the quality called fifteen-candle gas, will produce 3000 candle- light for one hour. But besides the product of gas, the coal yields certain bye products of almost equal value. I will, therefore, take it that we have, in effect, 1000 feet of gas from one cwt. of coal instead of from two, as is actually the case. And now, as regards the production of electricity. One cwt. of coal — that is the same measure in point of vcdue as gives 1000 feet of gas — will give 50 horse-power for one hour. Repeated and reliable experiments show that we can obtain through the medium of incan- descent lamps at least 200 candle-light per horse-power per hour. But as there is waste in the conversion of motive power into electri- city, and also in the conducting wires, let us make a liberal deduction of 25 per cent., and take only 150 candle-light as the nett available product of 1 horse-power; then for 50 horse-power (the product of 1 cwt. of coal), we have 7500 candle-light, as against 3000 candle- light from an equivalent vcdue of gas. That is to say, two and a half times more light. There still remains an allowance to be made to cover the cost of the renewal of lamps. There is a parallel expense in connection with gas lighting in the cost of the renewal of gas-burners, gas globes, gas chimnies, &c. I cannot say that I think these charges against gas lighting will equal the corresponding charges against electric lighting, unless we import into the account — as I think it right to do — the consideration that, without a good deal of expense be incurred in the renewal of burners, and unless minute attention be given, far beyond what is actually given, to all the conditions under which the gas is burned, nothing like the full light product which I have allowed to be obtainable from the burning of 1000 cubic feet of gas, will be obtained, and, as a matter of fact, is not commonly obtained, especially in domestic lighting. Taking this into account, and considering what would have to be done to obtain the full yield of light from gas and that if it be not done, then the estimate I have 40 Mr. Joseph W, Swan [March 10, made is too favourable, I think but little, if any, greater allowance need be made for the charge in connection with the renewal of lamps in electric lighting than ought to be made for the corresponding charges for the renewal of gas-burners, globes, chimneys, &c. But it will be seen that even if the cost for renewal of lamps should prove to be considerably greater than the corresponding expense in the case of gas, there is a wide margin to meet them before we have reached the limit of the cost of gas lighting. I think too it must be fairly taken into account and placed to the credit of electric lighting, that by this mode of lighting there is entire avoidance of the damage to furnishings and decorations of houses, to books, pictures, and to goods in shops, which is caused through lighting by gas, and which entails a large expenditure for repair, and a large amount of loss which is irreparable. I have based these computations of cost of electric light on the supposition that the light product of 1 horse-power is 150 candles. But if durability of the lamps had not to be considered, and it were an abstract question how much light can be obtained through the medium of an incandescent filament of carbon, then one might, with- out deviating from ascertained fact, have spoken of a very much larger amount of light as obtainable by this expenditure of motive power. I might have assumed double or even more than double the light for this expenditure. Certainly double and treble the result I have supposed can actually be obtained. The figures I have taken aie those which consist with long life to the lamps. If we take more light for a given expenditure of power, we shall have to renew the lamf>s oftener, and so what we gain in one way we lose in another. But it is extremely probable that a higher degree of incandescence than that on which I have based my calculations of cost, may prove to be compatible with durability of the lamps. In that case, the economy of electric lighting will bo greater than I have stated. In comparing the cost of producing light by gas and by electricity, I have only dealt with the radical item of coal in both cases. Gas lighting is entirely dependent upon coal — electric lighting is not, but in all probability coal will be the chief source of energy in the case of electric lighting also. When, however, water power is avail- able, electric lighting is in a position of still greater advantage, and, in point of cost, altogether beyond comparison with other means of producing light. To complete the comparison between the cost of electric light and gas light, we must consider not only the amount of coal required to yield a certain product of light in the one case and in the other, but also the cost of converting the coal into electric current and into gas ; that is to say, the cost of manufacture of electricity and the cost OF MANUFACTURE of gas. I caunot speak with the same exactness of detail on this point, as I did on the comparative cost of the raw material. But if you consider the nature of the process of gas manu- facture, and that it is a process, in so far as the lifting of coal by 1882.] on Electric Lighting hij Incandescence. 41 manual labour is concerned, not very unlike the stoking of a steam boiler, and if electricity is generated by means of steam, then the manual labour chiefly involved in both processes is not unlike. It is evident that in gas manufacture it would be necessary to shovel into the furnaces and retorts five or six times as much coal to yield the same light product as would be obtainable through the steam engine and incandescent lamps. But here again it is necessary to allow for the value of the labour in connection with the products other than gas, and hence it is right to cut down the difference I have mentioned to half — i.e. debit gas with only half the cost of manufacture, in the same way as in our calculation we have charged gas with only one- half the coal actually used. But when that is done, there is still a difference of probably three to one in respect of labour in favour of electric lighting. I have made these large allowances of material and labour in favour of the cost of gas, but it is well known that the bye products are but rarely of the value I have assumed. I desire, however, to allow all that can be claimed for gas. With regard to the cost of plant, I think there will be a more even balance in the two cases. In a gasworks you have retorts and furnaces, purifying chambers and gasometers, engines, boilers, and appliances for distributing the gas and regulating its pressure. Plant for generating electricity on a large scale would consist principally of boilers, steam engines, dynamo-electric machines, and batteries for storage. No such electrical station, on the scale and in the complete form I am supposing, has yet been put into actual operation ; but several small stations for the manufacture of electricity already exist in England, and a large station designed by Mr. Edison is, if I am rightly informed, almost comj)leted in America. We are therefore on the point of ascertaining by actual experience, what the cost of the loorJcs for generating electricity will be. Meanwhile, we know precisely the cost of boilers and engines, and we know approximately what ought to be the cost of dynamo-electric machines of suitably large size. We have, therefore, sufficient grounds for concluding that to produce a given quantity of light electrically the cost of plant would not exceed greatly, if at all, the cost of equivalent gas plant. There remains to be considered, in connection wdth this part of the subject, the cost of distribution. Can electricity be distributed as widely and cheaj)ly as gas ? On one condition, which I fully hope can be complied with, this may be answered in the affirmative. The condition is that it be found practicable and safe to distribute electricity of comparatively high tension. The importance of this condition will be understood when it is remembered that to effectively utilise electricity in the production of light in the manner I have been explaining, it is necessary that the resistance in the carhon of the lamps should be relatively great to the 42 Mr, Joseph W. Swan [March 10, resistance in the wires tvhich convey the current to them. When lamps are so united with the conducting wire, that the current which it conveys is divided amongst them, you have a condition of things in which the aggregate resistance of the lamps will be very small, and the conducting wire, to have a relatively small resistance, must either be very short, or, if it be long, it must be vei^y thick, otherwise there will be excessive waste of energy ; in fact, it will not be a practical condition of things. In order to supply the current to the lamps economically, there should be comparatively little resistance in the line. A waste of energy through the resistance of the wire of 10 or perhaps 20 per cent, might be allowable, but if the current is supplied to the lamps in the manner I have described — that of multiple arc, each lamp being as it were a crossing between two main ivires, then — and even if the individual lamps offered a somewhat higher degree of resistance than the lamps now in actual use — the thickness of the conductor would become excessive if the line was far extended. In a line of half a mile, for instance, the weight of copper in the conductor would become so great, in i^roportion to the number of lamps supplied through it, as to be a serious charge on the light. On the other hand, if a smaller conducting wire were used, the waste of energy and consequent cost would greatly exceed that I have mentioned as the permissive limit. Distribution in this manner has the merit of simplicity, it involves no danger to life from accidental shock ; and it does not demand great care in the insulation of the conductor. But it has the great defect of limiting within comparatively small bounds the area over which the power for lighting could be distributed from one centre. In order to light a large town electrically on this system, it would be necessary to have a number of supply stations, perhaps half a mile or a mile apart. It is evidently desirable to be able to effect a wider distribution than this, and I hope that either by arranging the lamps in series, so that the same current passes through several lamps in succession, or by means of secondary voltaic cells, placed as electric reservoirs in each house, it may be possible to economically obtain a much wider distribution. Whether by the method of multiple arc (illustrated by Diagram I.) which necessitates the multiplication of electrical stations; or by means of the simple series (illustrated by Diagram II.), or by means of secondary batteries connected with each other from house to house in single series, the lamps being fed from these in multiple arc (as illustrated by Diagram III.), I am quite satisfied that comj)aratively with the distribution of gas, the distribution of electricity is sufficiently economical to permit of its practical aj)plica- tion on a large scale. As to the cost of laying wires in a house, I have it on the authority of Sir Wm. Thomson, who has just had his house com- pletely fitted with incandescent lamps from attics to cellars— to the 1882.] on Electric Lighting hy Incandescence. 43 entire banishment of gas — that the cost of internal wires for the electric lamps is less than the cost of plumbing in connection with gas pipes. I have expended an amount of time on the question of cost which I fear must have been tedious ; but I have done so from the con- viction that the practical interest of the matter depends on this point. If electric lighting by incandescence is not an economical process, it is unimportant ; but if it can be established — and I have no doubt that it can — that this mode of producing light is economical, the subject assumes an aspect of the greatest importance. Although at the present moment there may be deficiencies in the apparatus for generating and storing electricity on a very large scale, and but little experience in distributing it for lighting purposes over wide areas, and consequently much yet to be learnt in these respects ; yet, if once it can be clearly established that light for light, electricity is as cheap as gas, and that it can be made applicable to all the purposes for which artificial light is required, electric light possesses such marked advantages in connection with health, with the preservation of property, and in respect of safety, as to leave it as nearly certain as anything in this world can be, that the wide substitution of the one form of light for the other is only a question of time. [J. W. S.] 4:i Eadiveard Muyhridye [Marcli 13, EXTRA EVENING MEETING, Monday, March 13, 1882. H.E.H. The Peince of Wales, K.G. F.R.S. Vice-Patron and Honorary Member, in tlie Chair. Eadweard Muybridge, of San Francisco. The Attitudes of Animals in Motion, illustrated with the Zoopraxiscope. The problem of animal mechanism has engaged the attention of man- kind during the entire period of the world's history. Job describes the action of the horse ; Homer, that of the ox ; it engaged the profound attention of Aristotle, and Borelli devoted a lifetime to its attempted solution. In every age, and in every country, philosophers have found it a subject of exhaustless research. Marey, the eminent French savant of our own day, dissatisfied with the investigations of his predecessors, and with the object of obtaining more accurate information than their works afforded him, employed a system of flexible tubes, connected at one end with elastic air-chambers, which were attached to the shoes of a horse ; and at the other end with some mechanism, held in the hand of the animal's rider. The alternate compression and expansion of the air in the chambers caused pencils to record upon a revolving cylinder the successive or simultaneous action of each foot, as it correspondingly rested upon or was raised from the ground. By this original and ingenious method, much interesting and valuable in- formation was obtained, and new light thrown upon movements until then but imperfectly understood. While the ^philosopher was exhausting his endeavours to expound the laws that control, and the elements that effect the movements associated with animal life, the artist, with a few exceptions, seems to have been content with the observations of his earliest jiredecessors in design, and to have accepted as authentic without further inquiry, the pictorial and sculptural rei)resentations of moving animals bequeathed from the remote ages of tradition. When the body of an animal is being carried forward with uniform motion, the limbs in their relations to it have alternately a progressive and a retrogressive action, their various portions acce- lerating in comparative speed and repose as they extend downwards to the feet, which are subjected to successive changes from a condition of absolute rest, to a varying increased velocity in comparison with that of the body. The action of no single limb can be availed of for artistic purposes without a knowledge of the synchronous action of the other limbs ; 188 2. J on Animals in Motion. 45 and to the extreme difficulty, almost impossibility, of the mind being capable of appreciating the simultaneous motion of the four limbs of an animal, even in the slower movements, may be attributed the innumerable errors into which investigators by observation have been betrayed. When these synchronous movements and the successive attitudes they occasion are understood, we at once see the simplicity of animal locomotion, in all its various types and alternations. The walk of a quadruped being its slowest progressive movement would seem to be a very simple action, easy of observation and presenting but little difficulty for analysis, yet it has occasioned interminable controversies among the closest and most experienced observers. When, during a gallop, the fore and hind legs are severally and consecutively thrust forwards and backwards to their fullest extent, their comparative inaction may create in the mind of the care- less observer an impression of indistinct outlines ; these successive a23pearances were probably combined by the earliest sculptors and painters, and with grotesque exaggeration adopted as the solitary position to illustrate great speed. Or, as is very likely, excessive projection of limb was intended to symbolise sjjeed, just as excess in size was an indication of rank. This opinion is to some extent cor- roborated by the productions of the Grecian artists in their best period, when their heroes are represented of the same size as other men, and their horses in attitudes more nearly resembling those possible for them to assume. The remarkable conventional attitude of the Egyptians, however, has, with few modifications, been used by artists of nearly every age to represent the action of galloping, and 23revails without recognised correction in all civilised countries at the present day. The ambition and perhaps also the province of art in its most ex- alted sense, is to be a delineator of imj)ressions, a creator of effects, rather than a recorder of facts. Whether in the illustrations of the attitudes of animals in motion the artist is justified in sacrificing truth, for an impression so vague as to be dispelled by the first studied observation, is a question perhaps as much a subject of con- troversy now as it was in the time of Lysippus, who ridiculed other sculptors for making men as they existed in nature ; boasting that he himself made them as they ought to be. A few eminent artists, notable among whom is Meissonier, have endeavoured in depicting the slower movements of animals to invoke the aid of truth instead of imagination to direct their pencil, but with little encouragement from their critics ; until recently, however, artists and critics alike have necessarily had to depend upon their observation alone to justify their conceptions or to support their theories. Photography, at first regarded as a curiosity of science, was soon recognised as a most important factor in the search for truth, and its more popular use is now entirely subordinated by its value to the astronomer, the anatomist, the pathologist, and other investigators of 46 Eadweard Muyhridge [March 13, the complex problems of nature. The artist, however, still hesitates to avail himself of the resources of what may be at least acknowledged as a handmaiden of art, if not admitted to its most exalted ranks. Having devoted much attention in California to experiments in instantaneous photography, I, in 1872, at the suggestion of the editor of a San Francisco newspaper, obtained a few photographic impres- sions of a horse during a fast trot. At this time much controversy prevailed among experienced horsemen as to whether all the feet of a horse while trotting were entirely clear of the ground at the same instant of time. A few ex- periments made in that year proved a fact which should have been self-evident. Being much interested with the experiments of Professor Marey, in 1877 I invented a method for the employment of a number of photo- graphic cameras, arranged in a line parallel to a track over which the animal would be caused to move, with the object of obtaining, at regulated intervals of time or distance, several consecutive impres- sions of him during a single complete stride as he passed along in front of the cameras, and so of more completely investigating the successive attitudes of animals while in motion than could be accom- plished by the system of M. Marey. I explained the plan of my intended experiments to a wealthy resident of San Francisco — Mr. Stanford — who liberally agreed to place the resources of his stock-breeding farm at my disj^osal, and to reimburse the expenses of my investigations, upon condition of my supplying him, for his private use, with a few copies of the con- templated results. The apparatus used and its arrangement will be better understood by a reference to the accompanying drawings. FIG.(. FIG. •4-. Fig. 1. A photographing lens, and camera containing a sensitised plate ; and side view of electro-exposor placed in front of camera. 1882.] on Animals in Motion. 47 Fig. 2. Back view of electro-exposor. Two shutters PP, eacli comprising two panels, with an opening O between them, are adjusted to move freely up and down in a frame ; they are here arranged ready for an exposure, and are held in position by a latch L and trigger T, all light being excluded from the lens. A slight extra tension of the thread B, Fig. 4, will cause a contact of the metal S23rings M S, and complete a circuit of electricity through the wires W W and the electro-magnet M ; the consequent attraction causes the armature A to strike the trigger, the latch is released, the shutters are drawn respectively upwards and downwards by means of the rubber springs S S, and light is admitted to the sensitised plate while the openings in the shutters are passing each other in front of the lens. Fig. 3. Front view of electro-exposor after exposure of the plate. Fig. 5. General view of studio, ojDcrating track, and background. In the studio are arranged 24 photograj)hing cameras at a distance of 12 inches from the centre of each lens ; an electro-exposor is securely fixed in front of each camera. Threads 12 inches apart are stretched across the track (only two of which are introduced in the Fig. 5. engraving), at a suitable height to strike the breast of the animal experimented with, one end of the thread being fastened to the back- ground, the other to the spring. Fig. 4, which is drawn almost to the point of contact. The animal in its progress over the track will strike these threads in succession, and as each pair of springs is brought into contact, the current of electricity thereby created effects a photographic exposure, as described by Figs. 2 and 4 ; and each consecutive expo- sure records the position of the animal at the instant the thread is struck and broken. For obtaining successive exposures of horses driven in vehicles, one of the wheels is steered in a channel over wires slightly elevated from the ground ; the depression of each wire completes an electric circuit, and effects the exposures in the same manner as the threads. 48 Eadweard Muyhridge [March 13, Fig. 6. Operating track, covered with corrugated indiariibber, and marked with transverse lines 12 inches apart. Each line is numbered, for the purpose of more readily ascertaining the length of the animal's stride. On one side of the track, and opposite to the battery of cameras, a white background is erected at a suitable angle. Fig. 6. The camera in which any one negative in a series of exposures is made is designated on that negative by the parallel direction of the vertical stake with the horizontal line extending to the corresponding number immediately oj)posite. The discriminating number of each series is marked on each negative by the large numbers — 229, for example — which are changed for each movement illustrated. For recording the successive attitudes of animals not under control, an apf)aratus is used, comprising a cylinder, around which are spirally arranged a number of pins ; uj)on the cylinder being set in motion through gearing connected with a spring or weight, these pins are consecutively brought into contact with a corresponding number of metal springs ; a succession of electric currents are thereby created which act through their respective magnets attached to the electro-exposors at regulated intervals of time. The cylinder is put in motion either by bringing it into gearing with other parts of the appa- ratus already in motion ; or by releasing a break with the hand, or by the action of some object at a distance by means of an electric current. This apparatus is principally used for illustrating the flight of birds, the motions of small animals, and changes of position without continuous progressive motion, such as occur during wrestling or turning a summersault ; when the cameras are directed towards the place where the movements are being executed. The boxes outside the studio (Fig. 5) contain cameras and electro- exposors for obtaining synchronous exj)osures of a moving object from different points of view. The following analyses of some of the movements investigated by 1882.] on Animals in Motion. 49 the aid of electro-photographic exposures, are repeated by permission of the President and Council from a paper read by the author before the Royal Society, and are rendered more perfectly intelligible by the reproductions of the actual motions projected on a screen through the zoopraxiscope. The Walk, Selecting the horse for the purposes of illustration, we find that during his slowest progressive movement — the walk — he has always two, and, for a varying period, three feet on the ground at once. With a fast walking horse the time of support upon three feet is exceedingly brief ; while during a very slow walk all four feet are occasionally on the ground at the same instant. The successive order of what may be termed foot fallings are these. Commencing with the landing of the left hind foot, the next to strike the ground will be the left fore foot, followed in order by the right hind, and right fore foot. So far as the camera has revealed, these successive foot fallings during the walk are invariable, and are probably common to all quadrupeds. But the time during which each foot, in its relation to the other feet, remains on the ground, varies greatly with different species of animals, and even with the same animal under different conditions. During an ordinary walk, at the instant preceding the striking of the left hind foot, the body is supported on the right laterals, and the left fore foot is in act of passing to the front of the right fore foot. The two hind feet and the right fore foot immediately divide the weight. The right hind foot is now raised, and the left hind with its diagonal fore foot sustains the body ; the left fore next touches the ground and for an instant the animal is again on three feet ; the right fore foot is immediately raised and again the support is derived from laterals — the left instead of as before the right. One half of the stride is now completed, and a similar series of alternations, substituting the right feet for the left, completes the other half. These movements will perhaps be more readily understood by a reference to the longitudinal elevation, Fig. 7, No. 1, which illustrates some approximate relative positions of the feet of a rapid walking horse, with a stride of 5 feet 9 inches. The positions of the feet indicated in this, and also in the other strides illustrated in Fig. 7 are copied from photographs, and from them we learn that during an ordinary walk the consecutive supporting feet are : 1. The left hind and left fore — laterals. 2. Both hind, and left fore. 3. Right hind and left fore — diagonals. 4. Right hind and both fore. 5. Right hind and right fore — laterals. 6. Both hind, and right fore. 7. Left hind and right fore — diarfonals. 8. Left hind and both fore. Vol. X. (No. 75.) e 50 Eadweard Muyhridge [March 13, 05 » » O w o W o CQ !?; o O l-H en p o o Q w o o s^ o H > >^ < l-H l-l O I s 03 o m P O P o ' o O o c3 O en >4 •l-H .!-( o t> M 03 <* S a O --( ""I -2 3 CQ i-K ^ & a s © d 1—1 rt fccg 02 *-" QQ -»^ _© " 2 en '+-I B ^ I-H OS CO to o CO CD in ^ CO